Hyperthermia

Prolonged immersion in hot water may induce hyperthermia.

Hyperthermia occurs when the internal temperature of the body reaches a level several degrees above the normal body temperature of 99ºF (37°C). The symptoms of hyperthermia include drowsiness, lethargy, and an increase in the internal temperature of the body. The effects of hyperthermia include:

Unawareness of impending hazard;
Failure to perceive heat;
Failure to recognize the need to exit hot tub;
Physical inability to exit hot tub;
Fetal damage in pregnant women; and
Unconsciousness and danger of drowning.

WARNING!
The use of alcohol or drugs can greatly increase the risk of fatal hyperthermia in hot tubs or spas.