Headache, Nausea, Dizziness, Fatigue… These Symptoms Could Be Altitude Sickness

1. Do You Know What’s Causing Your Discomfort?

Have you been feeling unwell lately without knowing why?

Perhaps your head feels heavy or throbs with pain. Maybe your stomach feels queasy and you have no appetite. You might feel dizzy when standing up, or unsteady on your feet when walking. Your body feels sluggish and you tire more easily than usual. At night, you struggle to fall asleep, or wake up repeatedly throughout the night.

If any of these symptoms sound familiar, take a moment to think back. Have you traveled anywhere in the past few days or weeks? Did you climb a mountain, visit a highland area, or take a long flight?

If something comes to mind, the discomfort you’re experiencing might be altitude sickness.

When people hear “altitude sickness,” many assume it’s a special condition that only affects serious mountaineers and alpinists—something that happens to people attempting Everest or Kilimanjaro, not something relevant to them.

However, altitude sickness is actually much closer to our daily lives than most people realize. Those who have climbed Mount Fuji, visited highland tourist spots like Tateyama or Norikura, traveled to South America or Tibet, or enjoyed skiing in Switzerland or Colorado—many of these travelers have experienced altitude sickness without even knowing it.

What might surprise you even more is that you can’t assume you’re safe just because you didn’t climb a mountain on foot. When you travel quickly to high elevations by car or ropeway, you can still develop altitude sickness even without climbing yourself. Additionally, airplane cabins are pressurized to levels lower than ground level, so some people experience altitude sickness-like symptoms during or after long flights.

In this article, we’ll explain in detail what altitude sickness is, what situations can trigger it, and how to prevent it. We’ll also cover what to do if you do develop altitude sickness, and discuss other conditions that can cause similar symptoms.

Whether you’re currently experiencing unexplained symptoms or planning a trip to high altitude destinations, please read through to the end.

2. Altitude Sickness Is More Common Than You Think

Before diving into the details of altitude sickness, let’s first understand just how common this condition really is.

Medically speaking, altitude sickness is defined as “a syndrome associated with hypoxia that occurs at high altitude.” Simply put, at higher elevations where the air contains less oxygen, the body cannot adapt to the environment and various symptoms appear.

Generally, the risk of developing altitude sickness increases at elevations above 2,500 meters (approximately 8,200 feet). However, some people may experience symptoms at elevations as low as 2,000 meters (6,500 feet). The important thing to understand is that altitude sickness is not a condition that only affects people with certain physical constitutions. It can happen to anyone, regardless of age, gender, fitness level, or athletic experience.

In fact, studies suggest that 30% to 50% of people who climb Mount Fuji experience some form of altitude sickness symptoms. Mount Fuji is one of Japan’s most popular climbing destinations, with people from Japan and around the world attempting to reach its summit every summer. A significant portion of these climbers suffer from headaches, nausea, and other symptoms.

So, in what specific situations might you develop altitude sickness? Let’s look at some typical scenarios.

Climbing Mount Fuji

Mount Fuji stands at 3,776 meters (12,388 feet), making it Japan’s highest mountain. Most climbers begin their ascent from the 5th Station (approximately 2,300-2,400 meters / 7,500-7,900 feet), but as they approach the summit, atmospheric pressure drops and oxygen levels decrease. The risk of altitude sickness is particularly high for those attempting “bullet climbing”—starting at night and climbing straight through to reach the summit for sunrise—as the body has no time to acclimatize to the altitude.

Highland Tourism Accessible by Car or Bus

Japan has many highland areas easily accessible by car, bus, or ropeway, including Mount Tateyama (approximately 3,000 meters / 9,800 feet), Mount Norikura (approximately 2,700 meters / 8,900 feet), and Kamikochi (approximately 1,500 meters / 4,900 feet). Because visitors don’t climb these places on foot, they may not be aware of the altitude sickness risk. However, rapidly ascending to high elevations in a short time can actually place greater stress on the body.

Long-Haul Flights

Aircraft cabins at cruising altitude are pressurized to approximately 0.8 atmospheres, equivalent to an elevation of roughly 1,800-2,400 meters (5,900-7,900 feet). As a result, some people experience headaches and fatigue during or after long flights. While this isn’t technically “altitude sickness” in the strict sense, similar mechanisms related to low pressure and reduced oxygen can trigger these symptoms. Those with pre-existing respiratory or cardiovascular conditions should be particularly cautious.

High-Altitude Travel Abroad

Many popular tourist destinations and cities around the world are located above 3,000 meters (9,800 feet). Cusco, Peru (approximately 3,400 meters / 11,200 feet), the gateway to Machu Picchu; La Paz, Bolivia (approximately 3,600 meters / 11,800 feet); and Lhasa, Tibet (approximately 3,650 meters / 12,000 feet) are all popular destinations where travelers are exposed to altitude sickness risk from the moment they arrive. Flying from Japan and stepping off the plane at an airport already above 3,000 meters places significant stress on the body.

Skiing and Tourism at High-Altitude Resorts

High-altitude ski resorts in places like Zermatt, Switzerland and Colorado, USA also pose altitude sickness risks. When focused on enjoying skiing or snowboarding, people often attribute their physical discomfort to tiredness or cold weather, overlooking the possibility of altitude sickness.

As you can see, altitude sickness is not just a concern for mountaineers. In today’s world where people travel to high elevations for tourism, leisure, and business, having accurate knowledge about altitude sickness is extremely important.

3. What Is Altitude Sickness?

Let’s take a closer look at what altitude sickness actually is.

At sea level where most of us live, the air contains approximately 21% oxygen. This oxygen concentration doesn’t change at higher elevations, but as atmospheric pressure decreases, the number of oxygen molecules in the same volume of air decreases. This means that with each breath at high altitude, the body takes in less oxygen.

For example, at the summit of Mount Fuji (3,776 meters / 12,388 feet), atmospheric pressure drops to approximately 63% of sea level. This means that even breathing normally, you can only take in about two-thirds of the oxygen you would at sea level.

Our bodies attempt to adapt to these low-oxygen environments in various ways. We try to breathe deeper and faster to increase oxygen intake, and our heart rate increases to deliver oxygen more efficiently throughout the body. Given time, the body can even produce more red blood cells to enhance oxygen-carrying capacity.

However, these adaptations take time. When we ascend too rapidly, the body cannot adapt quickly enough, and various symptoms appear. This is altitude sickness.

Altitude sickness can be broadly categorized into three types:

Acute Mountain Sickness (AMS)

This is the most common form of altitude sickness. The primary symptom is headache, often accompanied by nausea, dizziness, fatigue, and sleep disturbances. Symptoms typically begin 6-12 hours after arriving at high altitude. Mild cases often improve naturally with rest, but continuing activity while ignoring symptoms can lead to worsening conditions.

High Altitude Pulmonary Edema (HAPE)

This condition can occur when acute mountain sickness progresses or when altitude sickness presents severely from the onset. Fluid accumulates in the lungs, making breathing difficult. Characteristic symptoms include shortness of breath even at rest, coughing, and producing pink, frothy sputum. This is a life-threatening emergency requiring immediate descent and medical attention.

High Altitude Cerebral Edema (HACE)

This extremely dangerous condition involves swelling of the brain. Symptoms include severe headache, inability to walk straight (ataxia), confusion, and altered consciousness. This is also a life-threatening emergency requiring immediate descent and medical treatment.

A crucial point to understand about altitude sickness is that overconfidence—thinking “I’ll be fine”—is the most dangerous attitude. Even physically fit people and regular exercisers can develop altitude sickness. In fact, fit individuals may push themselves too hard precisely because of their fitness, worsening their condition. Even someone who had no problems at high altitude in the past may develop altitude sickness depending on their current health and condition. Susceptibility to altitude sickness varies between individuals and even within the same person at different times.

4. Understanding the Symptoms of Altitude Sickness in Detail

Let’s examine altitude sickness symptoms more closely. Understanding the characteristics of these symptoms will help you recognize early signs of trouble in yourself or your companions.

4-1. Mild to Moderate Symptoms (Acute Mountain Sickness)

Headache

Headache is the most common symptom of altitude sickness. Some statistics suggest that 80-90% or more of people who develop altitude sickness experience headaches.

Altitude sickness headaches can vary in character—some feel like throbbing, pulsating pain, while others feel like heavy pressure squeezing the entire head. The intensity can range from mild discomfort to severe pain that interferes with daily activities.

Characteristically, these headaches begin several hours after arriving at high altitude and tend to worsen at night and in the early morning. This is thought to be because breathing becomes shallower during sleep, leading to increased oxygen deprivation.

Nausea and Loss of Appetite

Gastrointestinal problems are also common with altitude sickness. Symptoms include general queasiness, loss of appetite, and actual vomiting.

These symptoms are thought to result from autonomic nervous system imbalances caused by low oxygen levels, as well as stimulation of the brain’s vomiting center. While you may not feel like eating, going without food can lead to decreased physical strength and worsening symptoms, so it’s important to consume small amounts of fluids and nutrients.

Dizziness and Unsteadiness

Feeling lightheaded when standing up, unsteady when walking, and foggy-headed are also characteristic symptoms of altitude sickness.

These symptoms signal that the brain is not receiving adequate oxygen. They tend to be stronger when standing up suddenly or after climbing stairs. Severe unsteadiness carries a risk of falls and injuries, so it’s important to stay still and rest rather than moving around unnecessarily.

Fatigue and Extreme Tiredness

At high altitude, even normal activities can make the body extremely tired. Symptoms include becoming breathless after walking just a short distance, feeling like the body is heavy and difficult to move, and experiencing overwhelming fatigue even without doing anything.

This occurs because the body is working hard in an oxygen-depleted environment. The heart works harder to pump more blood, and the lungs work harder to take in more oxygen. As a result, the body consumes more energy than usual, leading to increased fatigue.

Sleep Disturbances

Sleep quality often deteriorates significantly at high altitude. Many people experience difficulty falling asleep, waking multiple times during the night, waking due to breathlessness, or waking in the morning still feeling tired.

A particularly characteristic phenomenon is “periodic breathing,” which involves alternating between deep breaths and shallow breaths (or brief breathing pauses). This changing breathing pattern can cause the brain to awaken, disrupting sleep. The person may feel like they woke up because they couldn’t breathe, or they may not know why they woke up.

4-2. Warning Signs of Severe Illness (Dangerous Symptoms Not to Ignore)

If the following symptoms appear, altitude sickness may be progressing to a severe stage requiring emergency action.

Severe Headache

A headache that doesn’t respond to pain medication at all, or one that temporarily improves only to return severely, is a dangerous sign. Be particularly concerned if the pain feels unlike anything you’ve experienced before.

Repeated Vomiting

Vomiting not just once but repeatedly can lead to dehydration and electrolyte imbalances, causing rapid deterioration.

Shortness of Breath at Rest

While breathlessness during climbing or exercise is normal, persistent difficulty breathing while sitting or lying down may indicate high altitude pulmonary edema. Rapid, shallow breathing or inability to get relief from deep breaths are particular warning signs.

Coughing with Pink Sputum

Persistent dry coughing, or coughing that produces pink or blood-tinged frothy sputum, may indicate fluid accumulation in the lungs. This is a typical symptom of high altitude pulmonary edema and constitutes a life-threatening emergency.

Ataxia (Inability to Walk Straight)

Inability to walk straight on flat ground, needing to hold onto something to stand, or awkward hand and foot movements suggest possible high altitude cerebral edema. This is sometimes described as walking “like a drunk person.”

Altered Consciousness

Seeming dazed, slow to respond to questions, disorientation (not knowing what time it is or where you are), and confused speech are also warning signs of high altitude cerebral edema. The affected person often isn’t aware of these changes, so companions must watch for them.

If even one of these severe warning signs appears, immediately begin descending to lower elevation. If you’re climbing toward a summit, stop and begin descending. If you’re at a high-altitude lodge, try to move to a lower elevation lodge if possible. If you’re staying in a high-altitude city or resort, look for transportation to lower ground. Moving to lower elevation, even slightly, is the top priority. Seek medical attention as soon as possible.

5. How to Prevent Altitude Sickness

Proper preventive measures can significantly reduce the risk of developing altitude sickness. Here we’ll explain prevention strategies in detail, from the planning stages through actual activity at high altitude.

5-1. Prevention During Planning

The fundamental principle of altitude sickness prevention is “don’t rush.” The body needs time to adapt to low-oxygen environments, and allowing sufficient time for this adaptation is the most important preventive measure.

Allow Time for Acclimatization

Ideally, you should spend 1-2 days at elevations above 2,500 meters (8,200 feet) to let your body adjust before ascending higher. However, travel and climbing schedules are limited, and not everyone can afford this luxury.

Still, taking whatever time you can for acclimatization is important. For Mount Fuji climbs, for example, rather than starting to climb immediately upon arriving at the 5th Station, rest there for 1-2 hours to let your body adjust to the altitude. Many people skip this “5th Station rest” and start climbing right away, but this simple step can make a significant difference in altitude sickness risk.

Avoid Rushed Schedules

“Bullet climbing” should be particularly avoided. The style of departing from the 5th Station at night, climbing through the night, and descending by morning after seeing the sunrise leaves no time for the body to rest and greatly increases altitude sickness risk.

If possible, plan a schedule that includes an overnight stay in a mountain hut, allowing your body to rest while climbing. Climbing during daylight hours is also preferable for safety, as nighttime brings colder temperatures and reduced visibility.

Be Mindful of Ascent Rate

A well-known guideline for altitude sickness prevention is to “limit daily elevation gain to 500 meters (1,600 feet).” Of course, this is just a guideline and doesn’t apply to all situations, but the principle of avoiding rapid altitude gain is worth remembering.

When flying directly to high-altitude cities abroad, following this guideline is physically impossible. In such cases, avoid strenuous activity on the first day and take it easy to reduce stress on your body.

5-2. Prevention Through Health Management

Managing your health before departure is also essential for altitude sickness prevention.

Get Adequate Sleep

Sleep deprivation is one factor that increases altitude sickness risk. You may have trouble sleeping the night before a climb or high-altitude trip due to excitement, but try to get as much sleep as possible. At minimum, maintain a regular lifestyle in the days leading up to departure to keep your body in good condition.

Stay Well Hydrated

At high altitude, the body loses more water due to dry air, sweating from exercise, and faster breathing. Dehydration can worsen altitude sickness symptoms, so consciously maintain fluid intake.

As a guideline, it’s recommended to drink 250-500ml (about 8-17 oz) of fluids per hour during high-altitude activity. Rather than drinking large amounts at once, frequent small sips are more effective. Also, by the time you feel thirsty, you’re likely already mildly dehydrated, so drink consciously before you feel thirst.

Avoid Alcohol and Sleeping Pills

Alcohol promotes dehydration, reduces sleep quality, and suppresses breathing. All of these increase altitude sickness risk, so it’s advisable to avoid alcohol at high altitude, at least until your body has acclimatized. While “celebrating with a beer at the summit” may be appealing, it’s not advisable from an altitude sickness prevention standpoint.

The same applies to sleeping pills. Many sleeping pills suppress breathing, and their use at high altitude may increase altitude sickness risk. Avoid relying on sleeping pills just because you’re having trouble sleeping at high altitude.

Avoid Strenuous Exercise the Day Before

Exhausting yourself with strenuous exercise the day before climbing or high-altitude travel not only reduces your performance on the day but may also make you more susceptible to altitude sickness. Take it easy the day before departure to conserve your energy.

5-3. Prevention During Climbing or High-Altitude Stay

Your behavior after reaching high altitude is also important for altitude sickness prevention.

Move Slowly

“Don’t rush when climbing” is a cardinal rule of altitude sickness prevention. Specifically, the guideline is to maintain a pace that allows normal conversation while walking. If you’re so breathless that you can’t talk, you’re moving too fast.

At the beginning of a climb, when you still have energy, you may be tempted to walk quickly, but maintaining a slow pace from the start also helps conserve energy for later. Don’t rush; keep your own pace.

Take Frequent Breaks

Regular breaks are important not only for resting your body but also for allowing it to adjust to the altitude. Stop to rest every 30 minutes to an hour, and take time for hydration and light snacks.

Deep breathing during breaks is also effective. Consciously breathing deeply and exhaling slowly promotes oxygen intake and helps your body adapt.

Stay Alert to Changes in Your Condition

At high altitude, always pay attention to changes in how you feel. Don’t miss early symptoms like headache, dizziness, or nausea. Rather than thinking “It’s probably nothing” or “It’ll get better if I push through,” if you feel even slightly unwell, either rest, slow your pace, or consider turning back.

When traveling in a group, people often push themselves because they don’t want to inconvenience others or fall behind. However, letting altitude sickness worsen will ultimately cause greater inconvenience. If you feel unwell, don’t hesitate to tell your companions.

5-4. It Can Still Happen Despite Prevention

While we’ve covered various prevention methods, unfortunately, following all of them doesn’t completely eliminate the possibility of altitude sickness. Susceptibility to altitude sickness varies between individuals and is also affected by current health and condition.

Even someone who climbed the same mountain before without any problems may develop altitude sickness depending on their condition at the time. And some people may be constitutionally more prone to altitude sickness despite thorough prevention efforts.

What’s important is not to become discouraged thinking “Why did this happen when I was so careful?” but to respond appropriately when symptoms appear. In the next section, we’ll explain what to do if you develop altitude sickness.

6. What to Do If You Develop Altitude Sickness

Even with careful attention to prevention, altitude sickness can still occur. If you or a companion develops altitude sickness symptoms, how should you respond?

6-1. First Steps to Take

Stop Pushing Yourself

When altitude sickness symptoms appear, the most important thing is to stop pushing yourself. Continuing to climb or engage in activity while ignoring symptoms can lead to deterioration.

It’s natural to think “I’m almost at the summit” or “I’ve come this far,” but severe altitude sickness can be life-threatening. The mountain isn’t going anywhere. You can try again after your condition improves. Prioritize your own body first.

Descend to Lower Elevation

The most effective treatment for altitude sickness is descending to lower elevation. Simply moving from higher to lower ground can dramatically improve symptoms.

As a general guideline, symptoms often improve after descending 300-500 meters (1,000-1,600 feet). However, severe cases may require descending much further.

If you’re climbing, stop attempting to reach the summit and begin descending. If you’re at a mountain hut, consider moving to a lower elevation hut if possible. If you’re staying in a high-altitude city or resort, look for ways to get to lower ground.

Rest and Stay Calm

When descending isn’t feasible (for example, when it’s nighttime and travel would be dangerous), the next best option is to rest where you are. Lie down, relax your body, and focus on deep breathing.

During this time, carefully observe whether symptoms improve or worsen. If symptoms trend toward improvement, continue resting and prepare for descent the next morning. If symptoms worsen, you may need to consider ways to move safely even at night.

Take in Fluids and Nutrition

When experiencing altitude sickness symptoms, appetite tends to decrease, but dehydration and low blood sugar can worsen symptoms. Within reason, try to consume small amounts of fluids and carbohydrates.

6-2. Altitude Sickness Medication: Diamox (Acetazolamide)

Diamox (generic name: acetazolamide) is an effective medication for both treating and preventing altitude sickness. It is one of the few medications with established medical evidence for altitude sickness.

What Is Diamox?

Diamox was originally developed for treating glaucoma and as adjunct therapy for epilepsy, but it has been found to be effective for preventing and treating altitude sickness. It belongs to a class of drugs called carbonic anhydrase inhibitors, which work by affecting the body’s acid-base balance to help it adapt to high-altitude environments.

How It Works

Normally, our bodies are designed to increase breathing when blood carbon dioxide levels rise. However, in low-oxygen high-altitude environments, the body tries to breathe excessively to compensate, expelling too much carbon dioxide and causing the blood to become alkaline. In this state, the body responds by thinking “carbon dioxide is low, so I should breathe less,” which interferes with the adaptation process.

Diamox works by inhibiting the reabsorption of bicarbonate ions in the kidneys, keeping the blood slightly acidic. This allows the body to continue stimulating breathing, which improves oxygen uptake. Simply put, Diamox promotes and accelerates the body’s adaptation to high altitude.

Preventive Use

Diamox can also be used preventively for altitude sickness. It’s started 1-2 days before climbing or high-altitude travel and continued during the high-altitude stay or until sufficient acclimatization is achieved.

Preventive use is said to significantly reduce the risk of developing altitude sickness. It may be particularly recommended for those who have experienced altitude sickness before, those planning rapid altitude gain, and those who won’t have sufficient time for acclimatization.

Therapeutic Use

Diamox can also help reduce symptoms when altitude sickness has already developed. Of course, descending to lower altitude is the priority in severe cases, but combining Diamox can speed recovery.

Side Effects and Precautions

While Diamox is a relatively safe medication, you should be aware of some side effects.

The most common side effect is tingling or pins-and-needles sensations in the hands and feet (paresthesia). Many users experience this, but it’s usually mild and disappears when the medication is stopped. The medication also has diuretic effects, increasing urination frequency. This can increase dehydration risk at high altitude, so you need to be more conscious about fluid intake.

Some people also experience altered taste of carbonated beverages (finding them unpleasant). This is due to the medication’s mechanism and isn’t cause for concern, but if you were looking forward to a beer at the summit, it may taste different.

Rarely, more serious side effects such as severe allergic reactions can occur. Those with allergies to sulfa drugs (sulfonamide-class medications) in particular may experience similar allergic reactions to Diamox and should avoid taking it.

Prescription Required

In Japan, Diamox is classified as a prescription medication and cannot be purchased freely at pharmacies or drugstores. You need to see a doctor and obtain a prescription.

In some countries, it may be available over the counter, but self-medicating carries risks. Those with underlying medical conditions, those taking other medications, and those who are pregnant or breastfeeding should always consult a doctor before use.

Diamox Prescriptions at Our Clinic

Our clinic provides Diamox prescriptions for the prevention and treatment of altitude sickness. If you’re planning to climb Mount Fuji or travel to high-altitude destinations, or if you’ve experienced altitude sickness before and want to discuss measures for your next trip, please feel free to consult with us.

We also offer online consultations, so you can receive advice and prescriptions from the comfort of your home. Consulting well before your departure date will allow you to head to high altitude with peace of mind.

6-3. When to Seek Medical Attention

We recommend seeking prompt medical attention in the following situations:

Symptoms Don’t Improve with Rest

If symptoms don’t improve after descending and resting, or if symptoms persist for more than 24 hours, you may need medical evaluation and treatment. There may also be causes other than altitude sickness.

Symptoms Are Getting Worse

If symptoms gradually worsen despite resting, this is a dangerous sign. Seek immediate medical attention if headaches are intensifying, vomiting is becoming repetitive, or breathlessness is increasing.

Warning Signs of Severe Illness Are Present

If even one of the severe warning signs mentioned earlier (severe headache, shortness of breath at rest, coughing with pink sputum, inability to walk straight, altered consciousness) is present, this is an emergency. Descend as quickly as possible while arranging transport to a medical facility.

Symptoms Persist After Returning from High Altitude

If symptoms continue for several days after returning to low elevation from high altitude, causes other than altitude sickness should be considered. As explained in the next section, other conditions can produce symptoms similar to altitude sickness, so medical evaluation is recommended.

7. Is It Really Altitude Sickness?

While we’ve covered altitude sickness in detail, there are actually many other conditions that can cause similar symptoms. In this section, we’ll discuss other conditions that may be suspected based on the various symptoms of altitude sickness.

You may need to consider causes other than altitude sickness in the following situations:

• You have similar symptoms but haven’t been to high altitude recently
• Symptoms persist long after returning from high altitude
• Symptom patterns differ from typical altitude sickness progression
• You have other symptoms as well

7-1. Conditions Suggested by Headache

Headache is an extremely common symptom with various causes. Conditions other than altitude sickness that may cause headaches include:

Migraine

Migraines are characterized by throbbing, pulsating pain, often on one side of the head, though they can affect both sides. Sensitivity to light and sound, as well as nausea, are also common, which can make it difficult to distinguish from altitude sickness.

Some migraine sufferers experience visual disturbances called “auras” (such as seeing zigzag lights) before the pain begins. Stress, sleep deprivation, certain foods, and menstrual cycles can trigger migraines, so if any of these factors apply, migraine may be a possibility.

Tension Headache

Tension headaches feel like pressure squeezing the entire head, or like wearing a tight helmet. They’re often associated with shoulder and neck stiffness and tend to occur after desk work or long periods of driving.

During travel, long periods in the same position are common, creating conditions favorable for tension headaches. A headache experienced at high altitude might actually be caused by posture during travel.

Sinusitis

Sinusitis is inflammation of the sinuses (the air-filled spaces around the nose). It can cause pressure or pain in the forehead, cheeks, and behind the eyes, which may be perceived as a headache. It’s often accompanied by nasal congestion, yellow or green nasal discharge, and facial pressure.

Air pressure changes during flights can worsen sinusitis symptoms, so headaches after flying can be confused with altitude sickness.

Dehydration

Dehydration can cause headaches. At high altitude, increased water loss from dry air and exercise makes dehydration more likely. Signs of dehydration include dark urine, infrequent urination, and dry mouth.

Adequate hydration to resolve dehydration may improve headaches. It can be difficult to determine whether a headache at high altitude is purely from altitude sickness, dehydration, or both, but hydration is important regardless.

Meningitis (Emergency)

Meningitis is inflammation of the membranes covering the brain and spinal cord, causing severe headache. Characteristic symptoms include fever, neck stiffness (inability to touch chin to chest), and sensitivity to light.

Meningitis is a life-threatening emergency. If these symptoms are present, consider the possibility of meningitis rather than altitude sickness and seek immediate medical attention.

7-2. Conditions Suggested by Nausea and Vomiting

Acute Gastroenteritis/Food Poisoning

One of the most common causes of nausea and vomiting is acute gastroenteritis or food poisoning, which occurs after consuming food or water contaminated with viruses or bacteria. Diarrhea is common, and fever may also occur.

During travel, dietary changes make gastrointestinal problems more likely. When experiencing nausea at high altitude, consider not only altitude sickness but also the possibility of food-related causes.

Motion Sickness

Motion sickness causes nausea and dizziness during or after travel by car, bus, boat, or airplane. Travel to high altitude often involves long journeys on winding mountain roads, creating conditions favorable for motion sickness.

It can be difficult to distinguish whether nausea upon arrival is an early symptom of altitude sickness or lingering motion sickness. It’s important to rest and observe how symptoms change.

Heat Illness

Heat illness occurs when the body’s temperature regulation fails in hot environments. It causes nausea, dizziness, headache, and fatigue—symptoms very similar to altitude sickness.

While mountains may seem cool, climbing during summer days can lead to heat illness from direct sunlight and exercise-generated heat. It’s also possible to have both altitude sickness and heat illness simultaneously. Proper hydration, salt intake, and rest in cool environments are important.

7-3. Conditions Suggested by Dizziness and Unsteadiness

Benign Paroxysmal Positional Vertigo (BPPV)

BPPV causes brief episodes of spinning vertigo when changing head position. This might happen when getting up in the morning, looking up, or turning over in bed—a strong sensation of the world spinning.

This vertigo typically subsides within several seconds to a minute but can recur each time the head moves. It’s thought to be caused by small crystals called otoliths breaking loose and entering the semicircular canals of the inner ear.

Meniere’s Disease

Meniere’s disease is characterized by spinning vertigo, hearing loss, and tinnitus. Vertigo attacks can last from tens of minutes to several hours and may be accompanied by nausea and vomiting.

Symptoms often affect one ear, and hearing may gradually decline with repeated vertigo attacks. If dizziness is accompanied by tinnitus or hearing loss, Meniere’s disease should be considered.

Orthostatic Hypotension

Orthostatic hypotension occurs when blood pressure drops suddenly upon standing from a seated or lying position. Characteristic symptoms include lightheadedness, unsteadiness, and vision darkening.

Dehydration makes orthostatic hypotension more likely. Combined with dehydration at high altitude, dizziness when standing may be more pronounced.

Anemia

Anemia is a condition where red blood cells or hemoglobin in the blood are insufficient. It causes dizziness, unsteadiness, fatigue, shortness of breath, palpitations, and pallor.

When anemic, the body’s oxygen-carrying capacity is already reduced, making it even more vulnerable to low-oxygen environments at high altitude. Those who chronically experience dizziness or fatigue should check for anemia before traveling to high altitude.

7-4. Conditions Suggested by Fatigue and Extreme Tiredness

Sleep Deprivation/Jet Lag

For international travel, jet lag-induced sleep deprivation may cause fatigue. It can take several days for the body clock to adjust to local time, during which you may not sleep well or may feel drowsy during the day.

On high-altitude trips, jet lag effects and altitude sickness effects can overlap, making it difficult to determine which is causing the fatigue.

Dehydration/Low Blood Sugar

Dehydration and low blood sugar can also cause significant fatigue. During travel, irregular eating and drinking schedules can lead to unknowing dehydration or low blood sugar.

Fatigue caused by these factors improves with adequate hydration and properly timed meals.

Hypothyroidism

Hypothyroidism occurs when thyroid hormone production is insufficient. It causes chronic fatigue, easy tiring, weight gain, cold sensitivity, constipation, and dry skin.

This condition often progresses gradually, and symptoms are often dismissed as “aging” or “just tired.” Those who chronically feel fatigued should consider getting tested.

7-5. Conditions Suggested by Shortness of Breath and Difficulty Breathing

Asthma

Asthma is a condition where airway inflammation causes the airways to narrow, making breathing difficult. Characteristic symptoms include shortness of breath, coughing, and wheezing (whistling or squeaking sounds when breathing).

Cold air and exercise can trigger asthma attacks, so they may occur during high-altitude climbing. Even those never diagnosed with asthma may experience asthma-like symptoms for the first time at high altitude.

Pneumonia

Pneumonia is an infection causing lung inflammation. It produces fever, cough, sputum, and shortness of breath. Symptoms can be similar to high altitude pulmonary edema, making distinction difficult.

If fever is present, infectious disease (such as pneumonia) should be considered rather than altitude sickness.

Heart Failure

Heart failure is a condition where the heart’s pumping function is reduced, preventing adequate blood delivery to the body. Characteristic symptoms include shortness of breath, fatigue, swollen legs, and difficulty breathing when lying down at night.

The low-oxygen environment at high altitude stresses the heart, so those with pre-existing heart conditions may experience worsening symptoms at high altitude. Those with a history of heart disease should consult a doctor before traveling to high altitude.

Panic Attacks

Panic attacks involve sudden intense anxiety accompanied by physical symptoms such as palpitations, shortness of breath, sweating, and trembling. You may feel like you “can’t breathe” or fear you might die.

Anxiety about altitude sickness symptoms can trigger panic attacks, and panic attack symptoms can be mistaken for altitude sickness. If hyperventilation is involved, consciously slowing your breathing can improve symptoms.

8. If You Have These Concerns, Please Consult Us

If you’ve read this far and have concerns about your symptoms, or if you’re planning a trip to high altitude or mountain climbing, please consult our clinic.

This Information Is for You If:

• You’ve returned from high altitude but continue to have headaches, dizziness, fatigue, or other symptoms
• You became ill during or after climbing and don’t know the cause
• You have symptoms such as headache, nausea, dizziness, or shortness of breath and are worried it might be altitude sickness
• You’ve felt unwell since traveling somewhere recently and want to investigate the cause
• You want to consult in advance about an upcoming high-altitude trip or Mount Fuji climb
• You’ve experienced altitude sickness before and want to discuss preventive measures for your next trip

What We Can Do

At our clinic, we carefully listen to your symptoms and provide appropriate examinations and consultations as needed. When altitude sickness is likely, we provide treatment and prescriptions appropriate to the severity of symptoms. When causes other than altitude sickness are suspected, we can also refer you to appropriate specialists.