Altitude sickness also known as acute mountain sickness (AMS) is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude.
Headaches, nausea, vomiting, loss of appetite, fatigue or weakness, swelling of hands, face and feet, nose bleeding etc are the primary symptoms of altitude sickness while the severe symptoms includes persistent dry cough, fever, shortness of breath even when resting, headache that does not respond to analgesics, unsteady gait, gradual loss of consciousness, increased nausea and vomiting, retinal hemorrhage.
Ascending slowly is the best way to avoid altitude sickness. Avoiding strenuous activity such as skiing, hiking, etc. in the first 24 hours at high altitude reduces the symptoms of AMS. Other way to prevent altitude sickness is Acclimatization. The pre-acclimatization helps the body to develop tolerance to low oxygen concentration before ascending to an altitude. It significantly reduces risk because less time has to be spent at altitude to acclimatize in the traditional way. Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. For high altitude climbers, a typical acclimatization regimen might be to stay a few days at a base camp, climb up to higher camp slowly, and then return to base camp.
The only reliable treatment, and in many cases the only option available, is to descend. However others treatments can also be used such as oxygen, acetazolamide, tea made from coca plant, steroids are helpful in curing altitude sickness.