Altitude sickness comes in three basic forms: acute mountain sickness, high-altitude pulmonary edema and high-altitude cerebral edema. Acute mountain sickness is the most common, as it affects more than 50 percent of people who ascend higher than 8,000 feet (2,400 meters) in a relatively short time span. It's caused by the lower levels of oxygen in the air at high elevations; your lungs can't take in as much oxygen as they're used to and your heart and lungs have to work harder to keep your blood oxygenated. Symptoms of acute mountain sickness include dizziness, fatigue, nausea, headaches and difficulty sleeping. Acute mountain sickness usually goes away within a few days as long as you remain well hydrated and stay at the same altitude until the symptoms pass.
Among the ways people have traditionally relieved the symptoms of mild altitude sickness is through tea made of the coca leaf. Many workers in Central and South America who spend time at high altitudes use coca leaves to alleviate the discomfort. However, coca is a controlled substance in the United States; it's the same plant that's used to make cocaine. Over-the-counter medications are also available for the treatment of altitude sickness. Plus, some people like to use herbs like gingko bilboa to treat mountain sickness; however, there's no reliable scientific evidence that gingko does anything for altitude sickness.
In rare cases, acute mountain sickness doesn't pass; instead, it worsens and becomes a form of high-altitude edema, particularly among people who continue to ascend despite acute mountain sickness. When the symptoms don't go away and intensify, or they include shortness of breath, elevated heart rate, imbalance, confusion or seizures, it's time to worry. Both high-altitude pulmonary edema and high-altitude cerebral edema can be fatal and necessitate immediate descent to a lower altitude and urgent medical treatment.