Mountain sickness: nausea and shortness of breath experienced by mountain climbers above eight thousand feet.

Also known as altitude sickness or altitude illness, this is a disorder caused by being at high altitude, commonly above 8,000 feet (2,440 meters).

High altitude and lower air pressure cause fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain. Continuing to higher altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses.