You might be suffering from Acute Mountain Sickness (AMS). Usually striking at around 8,000 feet (2,450 meters) in altitude, AMS is your body's way of coping with the reduced oxygen and humidity of high altitudes. Among the symptoms are headaches, shortness of breath, loss of appetite, insomnia and lethargy. Some people complain of temporary weight gain or swelling in the face, hands and feet.
You can reduce the effect of high altitude by being in top condition. If you smoke or suffer from heart or lung ailments, consult your physician before your trip. Certain drugs will intensify the symptoms. To avoid Acute Mountain Sickness, adjust to elevations slowly; a gradual ascent with a couple days of acclimatization is best if you have time. For example, if you are planning a trip to the Rocky Mountains of Colorado, you might want to spend the first night in a lower altitude city such as Denver as opposed to heading directly to an environment with extreme elevations.
On the way up, eat light, nutritious meals and stay hydrated by drinking a large amount of water and taking care to avoid caffeine, alcohol and salt. In addition, your doctor may be able to prescribe medication that can offset the effects at high altitude.
If you develop AMS, you should stop ascending; you will recover in a few days. If the AMS is mild, a quick descent will end the suffering immediately.
Other high-altitude health problems include sunburn and hypothermia. Dress in layers to protect yourself from the intense sun and wide fluctuations in temperature.
Finally, after you lounge in the sauna or whirlpool bath at your lodgings, remember to stand up carefully, for the heat has relaxed your blood vessels and lowered your blood pressure.