Blood vessels in the skin become so dilated to promote internal cooling that blood to the brain and other vital organs is reduced to inadequate levels. Symptoms include nausea, dizziness, mild confusion, headache, mild temperature elevation, and dehydration. In advanced cases, the hyperthermic victim may or may not be sweating, and the skin may be cool to the touch. Cool the victim immediately by seeking shade and shelter. Ascending to high elevations without acclimating may produce headaches, fatigue, loss of appetite, drowsiness, and apathy.
Treatment includes rest, adequate consumption of fluids and food, and pain relievers.
If you're visiting from low elevations, proceed very slowly at first or allow an extra day to adjust to the new environment. Even the clearest mountain streams may be unhealthy to drink because of mine wastes, bacteria and viruses, or a single-celled organism called Giardia lamblia. This microorganism causes intestinal distress in the way of severe diarrhea, nausea, cramps, and loss of appetite. In short, it will make your life miserable for weeks if not treated medically. It becomes introduced to surface waters from animal and human waste.