@christym: Heat exhaustion can be considered as a warning to your body that you are getting too hot. Once it leads to heat stroke, your actual organs start to overheat. If they get too hot, they will simply stop working.
The symptoms for heat exhaustion and heat stroke are different. Obviously, the symptoms for the heat stroke are much more severe.
Some of the symptoms for heat exhaustion are: weak or rapid pulse, nausea or vomiting, muscle cramps, fatigue, weakness, dizziness, dry mouth, headache, cool or clammy skin, and sweating. Oddly enough, your body temperature will be normal or only slightly elevated.
With a heat stroke, you will usually have a very high temperature, usually 104 degrees or higher. You will also have red, hot, and dry skin, rapid pulse, confusion, hallucinations, convulsions, and loss of consciousness.
Heat stroke is a very serious, life-threatening emergency.