"Moutain sickness" refers to a series of symptoms that people can experience when they go to high altitudes where the air is thinner. These symptoms may include headache, dizziness, nausea, and difficulty breathing. Full definition
The first acute stage is called, naturally enough, acute mountain sickness. (scientificamerican.com)
The expedition had no major mishaps, and none of the 12 professional climbers evinced any obvious signs of high - altitude illness; the only acute case of mountain sickness was a mild one in the expedition's amateur climber. (scientificamerican.com)
A superficially related condition is chronic mountain sickness, also known as Monge's disease, occurring only after prolonged exposure to high altitude. (sastravelperu.com)