AMS, HAPE and HACE on a Nepal Trek: When Your Guide Says Descend

Updated 19 October 2026.

Short answer: Altitude illness comes in three forms. Acute mountain sickness (AMS) is common and usually mild: a headache plus nausea, dizziness, tiredness or no appetite. High-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema (HAPE) are rare and dangerous, and both mean you go down now. The rule on every trek I run is the same: if you have symptoms, you do not climb higher to sleep, and if they get worse, you descend. When your guide says descend, you descend.

I am Shreejan. My family has guided in these mountains for three generations, and the hardest conversation on a trek is always the same one: a strong, fit trekker who feels bad and does not want to turn back. This page is what I would want you to read before you ever have that conversation.

I am not a doctor, and this is not medical advice. The medical facts below come from the US Centers for Disease Control and Prevention (CDC) Yellow Book chapter on high-altitude travel and altitude illness, which I read on 19 October 2026. Talk to your own doctor before you travel.

What are AMS, HACE and HAPE?

The CDC describes headache as the main symptom of AMS, usually with at least one of the others. It says symptoms typically start 2 to 12 hours after you arrive at a high altitude. That is why the first night at a new height is the one to watch, and why your guide asks how you slept as soon as you wake.

What should I do if I get a mild headache?

Tell your guide. Do not hide it, even if it feels minor. Then:

The CDC puts the core rule in one line: never ascend to sleep at a higher altitude when you have symptoms of altitude illness, no matter how minor. I follow this on every trek. It is the reason our plans have rest days built in.

How far down is far enough?

The CDC says AMS improves quickly with a descent of 300 m (1,000 ft) or more, and it says to descend if symptoms become worse despite rest or treatment at the same altitude. For HACE and HAPE, go down immediately, and do not send the person down alone. On a trek, that means your guide goes down with you. If you cannot descend on foot, a helicopter evacuation is arranged through your travel insurance. That is why I ask every guest for an insurance policy that covers helicopter rescue to the highest point of the trek. Read travel insurance for Everest Base Camp before you buy.

Is it my fitness? Can I be too fit for AMS?

No. Fitness helps you walk, but it does not protect you from altitude illness. Young, strong trekkers often get into trouble because they walk fast, feel good and gain height quickly. The speed of your ascent matters more than your fitness. If you are worried about this, read scared of altitude, can I still trek Nepal.

What is the ascent rule I should follow?

The CDC advice is to avoid going from low altitude to a sleeping altitude of 2,750 m or more in a single day, and once you are above 3,000 m, to raise your sleeping altitude by no more than 500 m a night. It also advises a rest day every few days.

On our 12-day Everest Base Camp trek the plan has a full rest day at Namche Bazaar (day 3) and another at Dingboche (day 6). They are there because of this rule, and I do not want guests skipping them to save money. You can read the details in the 12-day Everest Base Camp trek and in altitude sickness on Nepal treks and how to prevent it.

What about Diamox and other medicines?

Some people take acetazolamide (Diamox) to help prevent altitude illness, and the CDC lists it as an option. It is a prescription drug with side effects, and it is not a substitute for a slow ascent. Ask your own doctor. I have written the longer version in Diamox and altitude medication for Nepal treks.

What do my guides carry and do?

Every trek we run carries a first-aid kit and a pulse oximeter, and our guides are trained to watch for altitude illness. The oximeter is one tool among several. Your guide also looks at how you walk, how you talk and whether you are eating. I explain why in pulse oximeters on Nepal treks. For the highest trips, such as Mera Peak, emergency oxygen is carried on the climb.

Frequently asked questions

What are the first signs of altitude sickness? A headache, usually with a poor appetite, dizziness, tiredness, nausea or poor sleep. Tell your guide at once.

How quickly does altitude sickness start? The CDC says symptoms typically begin 2 to 12 hours after arriving at a high altitude, so the first night at a new height is the one to watch.

What is the difference between AMS, HAPE and HACE? AMS is the common, mild form. HAPE is fluid in the lungs, with cough and breathlessness. HACE is swelling of the brain, with confusion and unsteady walking. HAPE and HACE are emergencies.

How far do you have to descend? For AMS, the CDC says a descent of 300 m (1,000 ft) or more brings quick improvement. For HAPE and HACE, you go down immediately as far as your guide and doctor advise.

Can I keep walking with a mild headache? You can keep walking at the same height, slowly. You must not go higher to sleep until the symptoms are gone.

Can a child or an older person trek safely? Altitude illness can affect anyone at any age. Tell me ages and health history and I will tell you honestly which trek fits. See the Everest Base Camp age limit.

Do I need travel insurance for altitude illness? Yes, and it should cover helicopter evacuation up to the highest point of your trek. Buy it at home, before you travel.

Will you refuse to let me continue if I am unwell? Yes. If my guide judges it unsafe, we stop or we go down. I would rather lose a day, or a summit, than lose you.

How do payment and cancellation work?

You pay a deposit of 10 per cent to book and the balance when you meet us in Kathmandu, in US dollars or euros, in cash or by card. Cash carries no fee, and card carries a 3.5 per cent bank charge. We cannot take Nepali rupees from foreign guests.

The deposit is non-refundable, and there is no refund if you cancel yourself. I can move your trip free of charge to any date within one year, with at least 72 hours notice. If we cannot run the trip, we refund what you have paid, less taxes, bank or card charges and any money already spent on your behalf.

What is the next step?

If you are planning a high trek and want to talk through the acclimatisation plan, message me on WhatsApp on +977 9810351300 with your dates and the highest you have slept before. I will tell you honestly what I think.

Medical source: CDC Yellow Book, High-Altitude Travel and Altitude Illness, read 19 October 2026.

Written by Shreejan Simkhada, CEO of The Everest Holiday, from a family of three generations of family guides. TAAN Member #1586. WhatsApp +977 9810351300.