Once you become hypothermic, you get fast pulse, low blood pressure, extreme weakness, dizziness, vomiting, and diarrhea which can progress to heat stroke. The stroke brings neurologic problems like confusion and seizures (at 104° Farheneit). If the temperature isn't reduced at that stage, irreversible damage can occur.

Body's enzymes are designed to be active at specific temperature ranges. If the body gets too hot, enzymes stop working and cells die. Kidney, lungs and nervous systems stop to function. At that point, a person can die very quickly if not cooled down immediately.