Acute Mountain Sickness: Symptoms and Prevention

Acute mountain sickness (AMS) is not rare in Leh. Most first-time visitors feel something in the first 24 hours — a dull headache, unusual fatigue, a vague sense that the body is doing more work than the situation seems to warrant. That is AMS, in its mild and completely normal form. It is your body responding to reduced oxygen at altitude, not a sign that something has gone wrong.

Understanding AMS before you arrive matters — not because it should frighten you, but because people who understand what's happening manage it far better than those who don't. The difference between a first-timer who rests, drinks water, and lets their body adapt, and one who pushes through the first day trying to be fine, is usually the difference between a smooth acclimatisation and a prolonged miserable one.

This guide covers the symptoms, the spectrum of severity, what actually prevents AMS, and what to do if symptoms progress. It is information — not medical advice. For specific health conditions or concerns, speak with a doctor before travelling to altitude.

What AMS is and why it happens

At Leh's altitude of 3,500m, atmospheric pressure is significantly lower than at sea level. Oxygen still makes up about 21% of the air — that doesn't change with altitude — but the total pressure means each breath delivers fewer oxygen molecules than you're used to. Your body responds by breathing more deeply and more frequently. Your kidneys adjust blood chemistry. Your heart rate increases modestly. All of this is normal and adaptive.

AMS occurs when this adjustment process is overwhelmed — typically because of rapid ascent, insufficient acclimatisation time, or individual susceptibility. The brain is particularly sensitive to changes in oxygen and blood chemistry, and most AMS symptoms are neurological in origin: the headache, the fatigue, the cognitive fuzziness that many people notice in the first days at altitude.

The Lake Louise Criteria, the standard clinical scoring system for AMS, requires headache plus at least one of the following: fatigue or weakness, dizziness or lightheadedness, gastrointestinal symptoms (nausea, vomiting, loss of appetite), or difficulty sleeping. Mild AMS on this scale is common — by some estimates, the majority of people flying directly to Leh experience it to some degree.

AMS symptoms — what to look for

In rough order of how they typically appear:

• Headache — usually the first and most reliable sign. It can be mild and dull, or more severe. It tends to worsen with exertion and improve with rest and hydration. This alone, without other symptoms, is normal in the first 24 hours at Leh.
• Fatigue and weakness — feeling more tired than the day's activity justifies. Unusual for people who are normally energetic. Expected in the first 1–2 days.
• Dizziness or lightheadedness — particularly on standing up quickly or moving suddenly. Often transient and manageable.
• Loss of appetite or nausea — common in the first 24–48 hours. Not severe in mild AMS; eat lightly rather than forcing meals.
• Sleep disruption — difficulty falling asleep, waking frequently, vivid or disrupted dreams. Sleep at altitude is physiologically different, particularly in the first few nights. This is normal.

These symptoms typically peak in the first 24–48 hours and resolve as acclimatisation progresses. By day three or four in Leh, most visitors feel substantially better. If symptoms are improving and you're not ascending further, you're likely acclimatising normally.

The severity spectrum — when to take it seriously

AMS exists on a spectrum. Mild AMS — headache, fatigue, mild nausea — is common, manageable, and resolves with time. At the other end of the spectrum are two serious conditions that are medical emergencies: High Altitude Cerebral Oedema (HACE) and High Altitude Pulmonary Oedema (HAPE). These are rare but genuinely dangerous, and the appropriate response is immediate descent and medical attention.

The rule of thumb with altitude illness is simple: never ascend with AMS symptoms. If you feel worse, or if symptoms are not resolving, descend. Descent is the most reliable treatment for altitude illness at any severity. Even a modest drop in altitude — a few hundred metres — produces measurable improvement in serious cases.

Who gets AMS — and the fitness myth

Fitness does not protect against AMS. This is the most persistent misconception about altitude sickness, and it sends fit, confident people into difficulty at altitude because they didn't expect to be affected. AMS susceptibility is largely individual and genetic — some people acclimatise easily and quickly; others, regardless of how fit they are, struggle more. Previous experience at altitude is the best predictor of how you'll respond, but it's not perfectly reliable either.

Age matters somewhat — younger adults may be slightly more susceptible, though this is inconsistent in the research. Being well-rested and well-hydrated on arrival helps. Ascending slowly is the most reliable preventive measure. But fitness level, yoga practice, endurance sport background, or physical strength are not meaningful protective factors against AMS. Respect the altitude regardless of how good you feel.

What actually prevents AMS

Diamox — what the evidence says

Acetazolamide (Diamox) is a carbonic anhydrase inhibitor that accelerates acclimatisation by increasing respiratory rate. It is used both as prophylaxis (taken before ascending) and as treatment for mild-to-moderate AMS. The evidence for its effectiveness is genuine — multiple controlled trials have shown that it reduces AMS incidence and severity in people ascending rapidly.

It also has side effects: increased urination, tingling in the fingers and toes, and a flattening of the taste of carbonated drinks. Some people find these manageable; others find them disruptive. It is a sulfa-based drug and is contraindicated for people with sulfa allergies. It is not appropriate as a substitute for slow ascent — taking Diamox while ascending too rapidly and ignoring AMS symptoms is not a safe strategy.

Whether to take Diamox is a decision for you and your doctor. If you have a history of poor acclimatisation, are ascending rapidly with no intermediate stop, or have known risk factors, it's worth discussing. For most healthy people arriving in Leh by air and following sensible first-day protocols, it may not be necessary. This is a general informational summary — consult a doctor for personalised guidance.

The first 48 hours in Leh — a practical protocol

1. Arrive and go directly to your accommodation. Rest for the first two to three hours.
2. Drink water steadily throughout the day. Avoid alcohol.
3. If you have a headache, ibuprofen or paracetamol can help. Rest and hydration often resolve it within a few hours.
4. Eat light — don't force meals if your appetite is suppressed, but don't skip eating entirely.
5. An easy evening walk is fine; a hike to Shanti Stupa at sunset on arrival day is too much for most first-timers.
6. Sleep as best you can — expect lighter, more disturbed sleep than normal in the first nights. This is normal physiology, not illness.
7. Day two: gentle activity only. Short walks, cultural visits, orientation. Don't ascend higher until day two symptoms have resolved.

How The Ladakh Reset handles acclimatisation

The first two days of The Ladakh Reset are in Leh and are deliberately designed around acclimatisation. Day one includes a gentle orientation, a Shanti Stupa visit, and a market walk — nothing strenuous. Day two adds breathwork and movement sessions designed specifically for altitude adaptation, a monastery visit, and easy exploration. No one is being pushed into difficult physical activity while their body is still adjusting.

The progression to Pangong on day three, and then to Hanle on day five, is staged — each step in altitude comes after days of adjustment at the previous level. By the time the group is at 4,250m in Hanle, most people have had enough time to adapt to feel genuinely well at altitude rather than just managing symptoms.

The details page covers the health and altitude guidance for the retreat in full, including conditions that require a doctor's clearance and those that don't. The guide to altitude acclimatisation in Leh covers the physiology of what your body does over the course of a stay.