Most people with altitude sickness recover within one to three days, depending on whether they descend or stay put. Mild cases often resolve in 12 to 48 hours simply by not climbing any higher. If you head downhill, relief can come much faster, sometimes within hours. Severe forms of altitude sickness, however, can take weeks or longer to fully recover from and may leave lasting effects.
Mild Altitude Sickness: 1 to 3 Days
The most common form, acute mountain sickness (AMS), feels a lot like an alcohol hangover. Headache is the hallmark symptom, usually joined by nausea, fatigue, dizziness, or loss of appetite. These symptoms typically appear 2 to 12 hours after arriving at a high elevation, often during or after the first night.
If you stop ascending and rest at the same altitude, AMS generally resolves within 12 to 48 hours. Most people feel meaningfully better by day two and fully recovered by day three. The body needs this time to adjust its breathing rate and blood chemistry to the thinner air. Within the first 44 hours at altitude, your kidneys begin flushing out bicarbonate (a natural buffering compound in your blood), which helps correct the chemical imbalance caused by breathing faster. That correction is what makes the symptoms fade.
How Descent Speeds Things Up
Dropping just 1,000 feet (about 300 meters) in elevation produces rapid improvement, especially if you keep physical exertion to a minimum during the descent. For many people, this means headache and nausea begin easing within an hour or two rather than over a full day. If supplemental oxygen is available, it can improve a headache in about 30 minutes and resolve other symptoms over the following hours, though oxygen is rarely accessible outside of medical facilities or organized expeditions.
Descent is the single most reliable way to shorten recovery. If your symptoms appeared at 12,000 feet and you drop to 11,000 feet, you’ll likely feel noticeably better by that evening. Returning all the way to the altitude where you last felt fine accelerates things further.
Severe Altitude Sickness: Weeks to Months
Two dangerous complications can develop from altitude sickness: fluid buildup in the lungs (HAPE) and swelling of the brain (HACE). Both are medical emergencies. HAPE causes breathlessness, a persistent cough, and extreme fatigue. HACE causes confusion, loss of coordination, and altered consciousness. Either can become fatal within hours if untreated.
Recovery from these severe forms is far less predictable. HACE in particular requires a greater descent than mild altitude sickness, and even with aggressive medical treatment, prolonged recovery times and permanent impairment are common. Some people experience lingering cognitive difficulties, memory issues, or coordination problems for weeks or months after the acute episode resolves. HAPE recovery tends to be somewhat faster once a person reaches lower elevation and receives oxygen, but full return to normal exercise capacity can still take one to two weeks.
Lingering Fatigue After Recovery
Even after the acute headache and nausea clear, many people notice residual tiredness for a day or two. This is normal. Your body has been working harder than usual: breathing faster, pumping more blood, and adjusting its internal chemistry. Think of it as a recovery debt. Staying well hydrated, eating normally, and sleeping a full night at a lower or stable elevation typically clears this lingering fatigue without any special intervention.
If fatigue or headaches persist beyond three or four days after descending, that warrants medical attention, as it may indicate incomplete recovery or a complication that wasn’t initially obvious.
When You Can Safely Climb Again
After a mild case of altitude sickness, you can generally resume ascending once your symptoms have fully resolved, not just improved. The key word is “fully.” Continuing upward while you still have a headache or nausea significantly raises the risk of progressing to a severe form. Once symptoms are completely gone, a cautious approach is to ascend no more than 1,000 to 1,500 feet per day in sleeping elevation, giving your body the gradual adjustment time it clearly needed the first time around.
If you experienced HAPE or HACE, returning to high altitude requires much more caution. Many high-altitude medicine specialists recommend waiting until you’ve been symptom-free for an extended period and, in the case of HACE, confirming that neurological function has returned to baseline before considering another ascent.
Factors That Affect Your Recovery Time
- How high you went. Symptoms are more intense and slower to clear at very high elevations (above 14,000 feet) compared to moderate ones (8,000 to 12,000 feet).
- How fast you ascended. Rapid gains in elevation, such as flying directly into a high-altitude city, tend to produce stronger symptoms that take longer to settle.
- Your hydration and rest. Dehydration and physical exhaustion both worsen symptoms and slow the body’s ability to acclimatize.
- Individual variation. Some people acclimatize quickly and recover in under a day. Others, at the same elevation, need the full three days. Fitness level does not reliably predict who adjusts faster.