heat stroke

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A severe condition caused by impairment of the body's temperature-regulating abilities, resulting from prolonged exposure to excessive heat and characterized by cessation of sweating, severe headache, high fever, hot dry skin, and in serious cases collapse and coma.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun illness caused by overheating the human body