The physical effect of being in a high-altitude environment. Abbreviated AMS, it is common at altitudes above 2,440 meters (approximately 8,000 feet). Three-fourths of people have mild symptoms of AMS at altitudes over 3,048 meters (approximately 10,000 feet). Occurrence depends on the altitude, rate of ascent, and individual susceptibility. Symptoms begin 12 to 24 hours after arrival at a new altitude and include headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and gen- eral malaise. These symptoms tend to worsen at night, when the respiratory drive is decreased. Symptoms should subside within 2 to 4 days, and can be treated by using pain medications such as aspirin. Acetazolamide (brand name - Diamox) can also be used to minimize symptoms and may be taken as a preventive measure. Moderate AMS has the same symptoms as AMS, but the headaches can- not be relieved with medication, and both breathing and coordinated movements become difficult. The only remedies are advanced medications and descent to lower altitudes. Severe AMS causes great shortness of breath at rest, inability to walk, decreased mental status, and fluid buildup in the lungs. Severe AMS requires immediate descent to lower altitudes 610 to 1,220 meters (approxi- mately 2,000 to 4,000 feet).