Headache and Nausea the First Night at Altitude? Altitude Sickness, and the Three Rules That Keep It Mild

Why arriving high makes you ill

The CDC chapter explains it simply: at around 3,050 m the oxygen in the air you breathe is only about 69 percent of what it is at sea level, and the body needs 3 to 5 days of acute acclimatisation to adjust. Illness can develop before that process is complete, and not afterward. Hypoxia is worst during sleep, which is why a day trip to altitude with an evening return lower is much easier on the body than sleeping high, and why sleeping altitude, not maximum altitude, is what matters.

Who gets it is partly genetic and not predictable by a test. CDC is clear that training and fitness make no difference, that sex plays little if any role, that children are as susceptible as adults and people over 50 slightly less so, and that any unacclimatised traveller sleeping at 2,450 m or higher is at risk. Some common destinations, Cusco and La Paz for example, put arriving travellers straight into a high-risk category because the airport itself is above 3,400 m; CDC notes that in those cases descending below the airport to sleep for a night or two can help.

What acute mountain sickness feels like

CDC's description: headache is the cardinal symptom, usually with one or more of loss of appetite, dizziness, fatigue, nausea or occasionally vomiting; onset 2 to 12 hours after arrival at altitude or after going higher, often during or after the first night; symptoms like an alcohol hangover; and it generally resolves within 12 to 48 hours if you do not ascend farther. Young children who cannot yet describe symptoms may go off their food, be irritable and pale.

Two useful checks from the chapter. First, there is no fever, runny nose, chills or muscle aches, so if those are present it is something else. Second, a descent of 300 m or more produces rapid improvement in AMS, which CDC notes is a useful confirmation that that is what it was. Symptoms that start more than three days after arrival, without further ascent, should not be put down to AMS.

The three rules

1. Know the early symptoms of altitude illness, which CDC says are the same as a hangover, and be willing to acknowledge when you have them.
2. Never ascend to sleep at a higher altitude while you have symptoms, no matter how minor they seem.
3. Descend if the symptoms become worse despite rest or treatment at the same elevation.

CDC's judgement on these is worth quoting in substance: because the onset and course of altitude illness are slow and predictable, there is no reason for anyone to die from it unless they are trapped by weather or geography where descent is impossible. The rules are not advice for mountaineers; they are for anyone sleeping high, including in a hotel in Cusco.

Treating the mild version

For AMS without the serious signs below, CDC says you can stay at your current altitude and treat the symptoms: rest, do not go higher, and use an ordinary painkiller such as ibuprofen or paracetamol for the headache and an anti-sickness medicine if needed. Oxygen helps if it is available, which it rarely is, and CDC notes the small handheld oxygen cans sold to tourists contain too little to make a sustained difference. Two prescription medicines are used in altitude illness: acetazolamide, which speeds acclimatisation, and dexamethasone, which relieves moderate to severe symptoms and is usually reserved for treatment alongside descent. Whether either is right for you, and at what dose, is a prescriber's decision; we deliberately do not give doses here.

The serious forms: when it is no longer a hangover

CDC describes two dangerous syndromes. High-altitude cerebral oedema, swelling of the brain, presents with neurological signs: altered mental state, unsteadiness or loss of coordination, confusion and drowsiness, similar to being drunk; CDC says coma can follow within 12 to 24 hours of the unsteadiness if it is not treated or the person does not descend. High-altitude pulmonary oedema, fluid in the lungs, starts as chest congestion, cough, breathlessness out of proportion to effort and falling performance, and progresses to breathlessness at rest and frothy or bloody sputum; CDC says it can be more rapidly fatal than the brain form and that in most circumstances descent is urgent and mandatory, with oxygen if available and as little exertion as possible.

Preventing it: pace, and sometimes a pill

• Ascend gradually. CDC's checklist: avoid going from low altitude straight to a sleeping altitude above 2,750 m in one day; once above 3,000 m, raise sleeping altitude by no more than 500 m a day, with an extra acclimatisation day for every 1,000 m gained.
• Acclimatising for 2 to 3 nights at around 2,450 to 2,750 m before going higher is, in CDC's words, markedly protective.
• No alcohol for the first 48 hours at altitude; keep to mild exercise for the first 48 hours; if you drink coffee, keep drinking it so a caffeine-withdrawal headache is not mistaken for altitude.
• Where the ascent cannot be gradual, for example flying into Cusco or La Paz, CDC says rates of altitude illness approach 50 percent and advises a low threshold for preventive medication. That is a conversation to have with a doctor before you go, or by video once you know your itinerary.
• CDC also advises caution for people with heart or lung conditions, sleep apnoea, or high-risk pregnancy, and suggests avoiding sleeping above roughly 3,050 m in pregnancy. If that is you, talk to a doctor before the trip.

You are already there: what this means in practice

Everything above is the CDC chapter. This section is ours. The realistic picture is a traveller in a hotel in Cusco, La Paz or Lhasa, or on the first nights of a trek, with a thumping headache and no appetite, wondering whether to push on with the itinerary. The honest answer from the chapter is: treat it like a hangover for a day, do not go higher to sleep tonight, and watch for the serious signs. Most people are fine by the second morning. The mistake is pressing on because the tour moves on; CDC's rule two exists for exactly that pressure.

Our country guides do not yet cover the high-altitude destinations in this chapter, which is why this article speaks generally. What does not change anywhere: a pulse oximeter costs little and CDC suggests travellers may want one to track acclimatisation, with the caveat that readings at altitude are expected to be lower than at home.

What a video doctor can and cannot do about this

A video consultation is one option for the first question: is this AMS, or something else? A doctor can take the history of your ascent, listen to the symptoms, look at you and at how you move and speak, check you against the serious signs, and tell you whether to sit tight and treat the headache, to take preventive or treatment medication you were prescribed before the trip, or to go down. If you were not prescribed anything and your itinerary forces a fast ascent, a doctor can advise on what is appropriate, where local rules permit.

What a video doctor cannot do is give you oxygen, measure your oxygen saturation for you, or get you down. If the serious signs are present, a consultation changes nothing about CDC's guidance: descend and get help.

The wider list of what a video consultation cannot do is in our guide to what cannot be treated with telemedicine.