Altitude & Acclimatization
Understanding altitude sickness — the most serious trekking risk.
Altitude sickness (acute mountain sickness) can affect anyone ascending above ~2,500m, regardless of fitness. It is the most serious common risk on Nepal's treks. Symptoms include headache, nausea, dizziness, loss of appetite and poor sleep.
The golden rule: ascend slowly. Build acclimatization days into your itinerary (Namche, Manang, Samagaon, Kyanjin), gain no more than 300–500m of sleeping altitude per day above 3,000m, and stay hydrated.
Mild symptoms can be managed by resting at the same altitude. Severe symptoms — worsening headache, vomiting, breathlessness at rest, confusion, or fluid in the lungs — require immediate descent. Never ascend with symptoms.
Consider discussing altitude medication (such as acetazolamide) with a doctor before your trip, but remember that medication is not a substitute for slow ascent. Carry insurance that covers helicopter evacuation. Take altitude seriously — it can be fatal.