An abnormally high fever, either in comparison to the normal body temperature of a specific disease or as in a heat stroke.

1. Heat stroke resulting from the prolonged exposure to the sun, characterized by extreme pyrexia, prostration, convulsion, and coma.
2. A severe and often fatal illness produced by exposure to excessively high temperatures; especially, when it is related to significant physical exertion.

It is usually experienced with elevated body temperature, lack of sweating, hot dry skin, and neurologic symptoms; including unconsciousness, paralysis, headache, vertigo, and/or confusion. In severe cases, very high fever, vascular collapse, and coma also develop.