Hypoxia

Hypoxia is a condition in which the body does not get enough oxygen to function efficiently.

Hypoxia is often associated with high altitudes, where it is called altitude sickness. This condition occurs because of the thinner (i.e., lower pressure) atmosphere at higher altitudes, which means the body takes in fewer oxygen molecules per breath. Symptoms of hypoxia include headaches, fatigue, shortness of breath, nausea, unsteadiness, and sometimes even seizures and coma.

Different people have different susceptibilities to hypoxia. For some otherwise healthy people symptoms can begin to appear at around 5000 feet (1500 meters) above sea level.