Acute mountain sickness is not a fitness problem. Marathon runners get it and sedentary people do not. It is a rate-of-ascent problem — which makes it, above all, an itinerary problem.
You can usually tell whether a trip will make people ill by reading the day list before you book.
The rule the good operators follow
Above 3,000 m, do not increase your sleeping altitude by more than 300–500 m per night, and take a full rest day every 900–1,000 m of gain.
Daytime highs matter far less than where you sleep. "Climb high, sleep low" is the whole principle.
Red flags in an itinerary
No dedicated acclimatisation day above 3,500 m. If the plan climbs steadily with no rest day, it was built for the calendar, not for you.
Manali to Kaza in one or two days. This is the classic Spiti mistake. You go from 2,050 m to a 4,590 m pass to sleeping at 3,800 m in about thirty hours. The Shimla approach spreads the same gain over four days and is dramatically safer.
Flying into Leh and driving to Pangong the next day. Leh is 3,500 m and Pangong is 4,350 m. Two full days doing very little in Leh first is not a wasted holiday — it is what makes the rest work.
A nine-day Goecha La. The standard is eleven, and the Dzongri acclimatisation day is what usually gets cut to make nine.
No oxygen or pulse oximeter carried above 4,000 m. Ask directly. A guide who hesitates has never needed it.
What the symptoms actually are
Mild AMS: headache, nausea, poor appetite, disturbed sleep, breathlessness on mild effort. Common, and it usually resolves if you stop ascending.
The two that mean descend now:
- HACE — confusion, unsteadiness, inability to walk heel-to-toe in a straight line. Test anyone who seems off.
- HAPE — breathlessness at rest, a wet cough, blue lips or fingertips.
Both are life-threatening and both improve with descent. Descent is the treatment. Everything else buys time.
Things people believe that are wrong
"I'm fit, I'll be fine." No relationship. Fit people ascend faster and get hit harder.
"I was fine last time." Susceptibility varies by trip. A clean record is not immunity.
"Diamox means I can skip acclimatising." Acetazolamide helps you acclimatise; it does not replace acclimatising. Discuss it with a doctor — it is a sulpha drug and has real side effects.
"Alcohol helps you sleep at altitude." It suppresses breathing and worsens dehydration. Not on ascent nights.
Practical, on the trek
Drink more than feels necessary — 3–4 litres a day. Eat carbohydrate even without appetite. Walk slower than you want to on the first days at a new altitude. Tell your guide immediately if you have a headache rather than after it becomes serious.
And tell the truth on the medical form. Guides make evacuation decisions using it.
The one question that filters everything
Ask an operator: "Where is the acclimatisation day, and what happens if someone develops symptoms?"
A good answer names the day and describes a descent plan. A vague answer is your signal to book elsewhere — because the same corner-cutting will show up at 4,500 m, when it costs a great deal more.