Acute mountain sickness

The higher you climb above sea level, the less oxygen there is to breathe. The oxygen level becomes very low at altitudes above 8,000 feet. People who normally live at or near sea level need to adjust to high altitudes because their bodies aren't used to working with so little oxygen.

Amnesia or memory loss that occurs at high altitudes may be due to:

bulletBrain swelling combined with oxygen deficiency (hypoxia)
bulletFluid accumulation (edema) in the lungs, which results in oxygen deficiency
bulletLow body temperature (hypothermia)
bulletPossible side effect of sleeping pills or dexamethasone (Dexamethasone Intensol, Decadron), a medication prescribed for people with prior severe cases of altitude illness
bulletOxygen deficiency even at moderate altitudes (13,000 to 14,000 feet)

Amnesia may also occur after descending from very high altitudes (above 16,500 feet). This may be due to lingering impairment of brain function due to brain swelling and oxygen deficiency.

The three main types of altitude illnesses are:

bulletAcute mountain sickness. Symptoms may include headache, dizziness, nausea and difficulty sleeping. If symptoms are mild, they usually disappear after a day or two at the same altitude. If symptoms persist, go down 2,000 to 3,000 feet until you feel better. The faster and higher you go, the more likely you are to develop acute mountain sickness.
bulletHigh-altitude pulmonary edema (HAPE). This causes fluid to accumulate in the lungs. Signs and symptoms include difficulty breathing even at rest, tightness in the chest, extreme fatigue and coughing. This requires prompt medical attention. You're more likely to get HAPE if you've had it before.
bulletHigh-altitude cerebral edema (HACE). This occurs when excess fluid accumulates in the brain (brain swelling). Signs and symptoms include confusion, difficulty with balance and coordination, and hallucinations. HACE requires immediate medical attention.

About 20 percent of people who climb to altitudes between 6,300 and 9,700 feet will develop mild symptoms of acute mountain sickness. Pulmonary and cerebral edema are rare at heights below 10,000. It's not clear why some people get acute mountain sickness and others don't.

To prevent acute mountain sickness:

bulletAscend slowly. Give your body time to adjust to the lower amount of oxygen. When you reach 8,000 feet, don't go up more than 1,000 feet a day.
bulletLimit physical activity over 8,000 feet.
bulletRest frequently.
bulletSleep at an altitude lower than the altitude you were at during the day.

Medications such as acetazolamide (Diamox, Dazamide) may also be used to prevent or treat severe mountain sickness.

 By Mayo Clinic Staff