What does altitude sickness feel like?

Most people describe it as a bad hangover. The CDC notes AMS symptoms resemble those of an alcohol hangover: a headache plus some combination of nausea, dizziness, fatigue, and loss of appetite. Poor sleep on the first night is also common.

How quickly does altitude sickness come on?

Usually fast. Symptoms typically begin 2 to 12 hours after reaching high elevation, often during or after your first night's sleep, so a headache the evening you arrive or the next morning is a common pattern.

At what altitude does sickness start?

Risk rises as you go higher. AMS commonly appears with sleeping altitudes above about 8,000 feet (2,450 meters); the CDC reports roughly 25% of visitors sleeping above that elevation in Colorado develop AMS, and more serious illness is linked to ascents above about 2,500 meters.

Is altitude sickness dangerous?

Mild AMS is usually not dangerous and resolves within a couple of days. But it can progress to HACE (brain swelling) or HAPE (fluid in the lungs), both of which are potentially fatal and need immediate descent and emergency care.

How do you get rid of altitude sickness?

For mild cases, rest, fluids, a pain reliever such as ibuprofen for the headache, and not climbing any higher until you feel better. Severe cases require oxygen, medication, and descent. The single most effective remedy for serious symptoms is going to a lower elevation.

Learning›Lifestyle & Skin Triggers

Altitude Sickness Symptoms: How to Spot Them and When to Worry

June 6, 2026

You drove or flew up to the mountains for a trip you were excited about, and a few hours in your head is pounding, you feel queasy, and you can't sleep. Before you write it off as a bad night or too much wine, you might be feeling the first signs of altitude sickness.

It is common, it is usually mild, and most people feel better within a couple of days. But altitude sickness also exists on a spectrum, and a small number of cases turn serious. Knowing which symptoms to expect and which ones mean it is time to come down can keep a great trip from becoming an emergency.

What are the symptoms of altitude sickness?

The most common form of altitude sickness is acute mountain sickness, or AMS. Its cardinal symptom is a headache, usually paired with at least one other complaint. According to the CDC, the overall picture closely resembles an alcohol hangover, which is why so many people mistake it for something they ate or drank.

Typical AMS symptoms include:

Headache (the hallmark sign)
Loss of appetite (anorexia)
Nausea or vomiting
Dizziness or lightheadedness
Fatigue and weakness
Disturbed or poor sleep

How soon do altitude sickness symptoms start?

Symptoms tend to come on within hours of arriving at high elevation, not days later. The CDC notes that onset is typically 2 to 12 hours after reaching high altitude, often during or just after your first night's sleep. Review literature from StatPearls describes a similar window of roughly 6 to 12 hours after ascending above about 2,500 meters (8,200 feet).

This timing is a useful clue. If a headache and nausea appear the evening you arrive or when you wake the next morning, altitude is a likely culprit. Altitude sickness is also common: the CDC reports that AMS affects about 25% of visitors who sleep above 8,000 feet (2,450 meters) in Colorado.

How long does altitude sickness last?

For most people, mild AMS is self-limiting. Symptoms usually ease on their own within a couple of days as your body acclimatizes to the thinner air, especially if you stop climbing higher and let yourself rest.

The key rule is to not ascend further until your symptoms have resolved. Pushing higher while you still feel sick is what allows a mild case to progress into something more dangerous. If you give your body time at the same elevation, the hangover-like feeling typically fades.

Mild AMS vs. severe altitude sickness (HACE and HAPE)

Altitude illness is a spectrum of increasing severity, and the difference between mild and severe is what every traveler should understand. AMS sits at the mild end. From there it can advance to two life-threatening conditions.

High-altitude cerebral edema (HACE) is swelling of the brain and the advanced stage of AMS. Warning signs are neurologic: trouble walking a straight line (ataxia), confusion, drowsiness, and altered mental status. High-altitude pulmonary edema (HAPE) affects the lungs, with fatigue, shortness of breath, and a dry cough that worsens with exertion and can progress to breathlessness even at rest. Both HACE and HAPE are potentially fatal and are medical emergencies.

How is altitude sickness treated?

Mild AMS often responds to simple measures. Rest, fluids, and an over-the-counter pain reliever such as ibuprofen for the headache are commonly used, along with avoiding further ascent until you feel better. Many people improve within a day or two using this approach.

Severe altitude illness is different and urgent. HACE and HAPE may require supplemental oxygen, medications such as dexamethasone, hyperbaric therapy, and, most importantly, descent to a lower elevation, which is the definitive treatment. This is general education, not a personal treatment plan, and any medication should be guided by a clinician who knows your history.

When to see a doctor or descend immediately

Plain rule: when in doubt, go down. Mild symptoms that improve with rest can usually be managed where you are, but certain signs mean you should descend and seek emergency care without delay.

Treat it as an emergency and get to lower elevation if you notice any of these:

Trouble walking, stumbling, or loss of coordination
Confusion, unusual drowsiness, or changes in behavior
Shortness of breath at rest, not just with effort
A cough that worsens or brings up frothy or pink fluid
Symptoms that keep getting worse despite resting and stopping your ascent

Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting any new skincare treatment, especially if you have underlying health conditions, are pregnant, or are taking medications.