altitude sickness

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A collection of symptoms, including shortness of breath, headache, and nosebleed, brought on by decreased oxygen in the atmosphere, such as that encountered at high altitudes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun medicine A pathological condition caused by oxygen deficiency at high altitudes; symptoms include shortness of breath, nausea, and nosebleed.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun effects (as nosebleed or nausea) of oxygen deficiency in the blood and tissues at high altitudes