Acute Mountain Sickness
Acute mountain sickness, or AMS, is a moderate threat encountered by travelers such as trekkers in the Himalayas or high-altitude back-country skiers. As you ascend, your body slowly acclimatizes to the higher altitude and thinner air. However, if you ascend too quickly and outstrip your body's ability to adjust, you develop AMS. The symptoms of AMS have been compared to a bad hangover and include headache, insomnia, dizziness, fatigue and loss of appetite. Descending is the best treatment for AMS.
High-Altitude Cerebral Edema
When AMS becomes life-threatening, it is called high-altitude cerebral edema (HACE). HACE symptoms include vomiting, lethargy, confusion, drowsiness, loss of coordination and coma. The condition can become fatal after a few hours or a few days. Because the hallmark of HACE is the impairment of cognitive ability, a person with HACE may be too impaired to realize what is wrong with him and to properly evaluate his situation. According to Altitude.org, anyone behaving in an irrational or bizarre way should be suspected of suffering from HACE. The site recommends having the person walk toe-to-heel in a straight line; if he fails the test you can presume he has HACE. To treat the condition, descend immediately.
High-Altitude Pulmonary Edema
AMS and HACE are the products of an oxygen-starved body. A different sort of high-altitude sickness is high-altitude pulmonary edema, or HAPE. This illness is the result of low air pressure causing a fluid build-up in the lungs. The condition can be fatal within just a few hours. HAPE is easily confused with AMS or HACE and it is possible for a person to suffer from HAPE and ACE/HACE at the same time. HAPE symptoms include lethargy, shortness of breath while resting or fast, shallow breathing, gurgling breaths, cough with a pink, frothy sputum, tightness or congestion of the chest, drowsiness and blue or gray lips and/or fingernails. Like HACE, HAPE is treated with immediate descent to lower altitude. If necessary, HAPE-sufferers can be placed in a Gamow bag, in which air pressure can be adjusted.