Hypothermia is a medical condition where the core body temperature of a body drops below the required temperature needed for normal body functions.
In 2268, Cervantes Quinn used a medical tricorder on himself and discovered that he was suffering from hypothermia and hypoxia. He cured the hypothermia with some tri-ox compound. (VAN - Declassified novella: The Stars Look Down)
In 2273, when the Federation SW7-class shuttlecraft Halley was damaged within the Hohweyn system, Doctor Leonard McCoy tried to prevent Pavel Chekov from getting hypothermia. (TOS novel: The Kobayashi Maru)