Visitors tour high altitude regions like Tibet often experience altitude sickness, which is caused by the low atmospheric pressure and thin air. Symptoms of altitude sickness are: nausea and dizziness, loss of appetite, shortness of breath, headache, excessive thirst, nervousness, rapid heart beat, nose bleed, general feeling of malaise, disturbed sleep and muscle pain.

Altitude sickness can occur in some people as low as 8,000 feet, but serious symptoms do not usually occur until over 12,000 feet.

It is difficult to determine who may be affected by altitude sickness since there are no specific factors such as age, sex, or physical condition that correlate with susceptibility. Some people get it and some people don't because some people are more susceptible than others.

Do not overexert yourself for the first 24 hours after arriving at a high altitude area. Give your body time to adjust or acclimatize. Keep in mind that different people will acclimatize at different rates. Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least four to six liters per day). Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating altitude sickness symptoms.

Avoid tobacco, alcohol and other depressant drugs including, barbiturates, tranquillizers, sleeping pills and opiates such as dihydrocodeine. Eat a high calorie diet.