It is generally thought that the loss of water from heavy sweating causes the cramps. Blood flow to the skin increases, causing blood flow to decrease to the vital organs. This result in a form of mild shock. If not treated, the victim's condition will worsen. Body temperature will keep rising and the victim may suffer heat stroke.
Heat stroke is life-threatening.
The victim's temperature control system, which produces sweating to cool the body, stops working. The body temperature can rise so high that brain damage and death may result if the body is not cooled quickly. Another term for heat stroke. If a Heat Wave Is Predicted or Happening . . . Avoid strenuous activity.