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 usually less serious condition, however it can progress to heat stroke if not recognized and treated properly.
There are two types of heat stroke: classic, non-exertional heat stroke (NEHS) and exertional heat stroke (EHS). Classic heat stroke happens most commonly to very young or older people, who have health risks and are in poor environmental conditions without access to air-conditioning and with limited access to fluids. Exertional heat stroke happens abruptly, more often to younger, healthy people who participate in strenuous physical activity.