Final answer:
Heat stroke is the most severe form of heat illness and can be life-threatening. It occurs when the body's temperature regulation mechanisms fail.
Step-by-step explanation:
The most severe form of heat illness, and a life-threatening emergency, is heat stroke. Heat stroke occurs when the body's temperature regulation mechanisms fail, leading to a dangerous increase in body temperature. Symptoms of heat stroke include a high body temperature, absence of sweating, rapid heartbeat, confusion, and loss of consciousness.
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