Hypothermia is a medical condition where the core body temperature of a body drops below the required temperature needed for normal body functions.
Cervantes Quinn used a medical tricorder in 2268 on himself and discovered that he was suffering from hypothermia and hypoxia. He was able to cure the hypothermia with some tri-ox compound. (VAN - Declassified novella: The Stars Look Down)
In the year 2273 when the Federation SW7-class shuttlecraft Halley was damaged within the Hohweyn system, Doctor Leonard McCoy was trying to prevent Pavel Chekov from getting hypothermia. (TOS novel: The Kobayashi Maru)
In 2368 Jean-Luc Picard and Geordi La Forge had to work quickly to prevent the Legarans from succumbing to hypothermia after a Romulan agent had sabotaged their environmental systems. (TNG short story: "Last Words")