As you gain altitude, the atmosphere thins and the partial pressure of oxygen in each breath drops — your body works harder for the same amount of oxygen. Acute Mountain Sickness (AMS) is what happens when your physiology has not caught up with your altitude: a headache is usually the first sign, often followed by fatigue, loss of appetite, nausea, dizziness or poor sleep. Most cases are mild and resolve with rest, fluids and time. Left unmanaged, though, AMS can progress to two much more serious and occasionally fatal conditions — High Altitude Pulmonary Edema (HAPE, fluid in the lungs) and High Altitude Cerebral Edema (HACE, swelling in the brain) — both of which require immediate descent and, often, emergency evacuation.
The single most effective prevention strategy is a slow, staged ascent that gives your body time to adapt. Guides commonly talk about not increasing your sleeping altitude by more than a few hundred metres a day once you are above roughly 3,000 metres, and building in a rest day every few days to let your body catch up . “Climb high, sleep low” — taking an acclimatization day-hike to a higher altitude before returning to sleep lower down — is a well-established way to trigger adaptation without adding overnight strain. The one rule that overrides everything else: if symptoms do not improve with rest, or get worse, the answer is to descend — not to push on and see if it passes. No summit, viewpoint or itinerary is worth the risk of HAPE or HACE.
Some trekkers use acetazolamide (commonly known by the brand name Diamox) to help ease acclimatization, but it is a prescription medicine with contraindications (including sulfa-drug allergy) and potential side effects, and any decision to use it — including dosage and timing — should be made with your own doctor before you travel, not decided on the trail . Alongside medication, the basics still matter most: drink more water than feels natural, avoid alcohol at altitude, eat even when your appetite dips, and tell your guide the moment you feel off rather than waiting to see if it passes. Lekali Journeys guides are trained to monitor the group for AMS symptoms and to arrange descent or evacuation without delay if it is needed — that is part of what a licensed guide is there for.
Beyond a simple headache, a handful of specific signs point toward the more dangerous HAPE or HACE and warrant immediate action rather than a wait-and-see approach:
Any one of these is a reason to descend without delay and seek medical attention — your guide is trained to recognise these signs and to act on them immediately, including arranging helicopter evacuation where necessary.
Acute Mountain Sickness affects up to 50% of trekkers above 3,500 m. Understanding the symptoms, prevention and treatment could save your trek — and in serious cases, your life.
Time your trek right and you might walk into a centuries-old festival: masked monastery dances, family reunions, or a chariot procession through Kathmandu. What to know.
New to trekking in Nepal? Honest answers to the questions we hear most often from first-time trekkers, before they have even booked a flight.
