Heat stroke is also known as sunstroke, thermic fever, or siriasis. It happens when the body's mechanisms for controlling temperature fail. Heat stroke is a life-threatening emergency needing immediate treatment. While many people feel sick and faint during heat waves, most of these people are suffering from heat exhaustion, a related condition usually less serious than heat stroke.
There are two types of heat stroke: classic, non-exertional heat stroke (NEHS) and exertional heat stroke (EHS). Classic heat stroke occurs most commonly in very young or older individuals, who have health risks and are in poor environmental conditions. Exertional heat stroke occurs more often in younger, healthy individuals who participate in strenuous physical activity.