While the first two can be painful and serious, heat stroke is a life-threatening condition. Although heat cramps can be painful, they don't cause permanent damage. To avoid them it is important to drink electrolyte solutions such as Gatorade or other sports drinks, in addition to plain water. Heat exhaustion is more serious than heat cramps and occurs when the body's cooling system begins to shut down. This happens when you don't drink enough fluids to replace what you are sweating away.
Heat exhaustion is usually the result of excessive heat and dehydration.
Because the body's cooling system has sent so much of its blood supply to the skin to cool it off, the supply to the brain is reduced. And this can cause confusion and sometimes unconsciousness. Other symptoms of heat exhaustion include dizziness, intense thirst, heavy sweating, fatigue, loss of coordination, nausea, vomiting, fainting, impaired judgment, weak and rapid pulse, low to normal blood pressure and a moderately increased temperature. Cool them down with air conditioning, cold wet cloths or fans and give them water or electrolyte drinks. Victims of heat exhaustion should avoid activity for at least a full day and should drink plenty of water to replace the lost body fluids.