Hypothermia is subnormal body temperature which can lead to mental and physical collapse and death. Hypothermia is caused by combinations of cold, wetness, and wind, and can be aggravated by exhaustion. Altitude Sickness is a result of overexertion at high elevations when oxygen supply is reduced. Hyperventilation is caused by rapid breathing and a decrease of carbon dioxide level in the blood, causing light-headedness and a cold feeling. A good principle to follow is to take it slow, rest often, move to lower elevation if necessary, snack frequently, and most important, drink a lot of fluids to restore body energy.
Dehydration is a lack of fluid intake.
Adults require two quarts of water daily and up to four quarts when exercising at high elevations. Emergencies can occur at anytime. If you get lost, take it easy, keep calm, don't panic. Sit down and figure out where you are. use your head and not your legs. You will want detailed maps for your trip.