Altitude sickness, also known as Acute Mountain Sickness (AMS), is a medical condition that can occur when a person quickly ascends to high altitudes, typically above 8,000 feet (2,438 meters). At higher altitudes, the air pressure and oxygen levels are lower, which can cause various symptoms as the body adjusts to the new environment.

Symptoms of altitude sickness can include headache, nausea and vomiting, dizziness, fatigue, shortness of breath, and difficulty sleeping. In severe cases, altitude sickness can lead to High Altitude Cerebral Edema (HACE) or High Altitude Pulmonary Edema (HAPE), which can be life-threatening if not treated promptly.

To prevent altitude sickness, it's important to acclimate gradually by spending a few days at intermediate elevations before going to higher elevations. It's also recommended to stay well hydrated, avoid alcohol and sleeping pills, and to avoid overexertion. Treatment for altitude sickness may include oxygen therapy, descent to lower altitude, or medication such as acetazolamide.