The best replacement for hypothermia is hyperthermia.

The best alternatives to hypothermia are rated as following:
★★★★★  hyperthermia
★★★  frostbite
★  frostfall
★  normothermia
★  water temp
  drowning
  torpor
  heat stroke
  water temperature

Your alternative for hypothermia is not listed? Suggest!
Speaking about hypothermia, one probably shouldn't forget about hypoglycemia.

Other search terms related to hypothermia and their ratings are:
★★★★★ hypoglycemia
★★★★ cardiac arrest
★ circulatory arrest
You have in mind a companion for hypothermia and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of hypothermia in all years. Click on graph for more.
hypothermia
hyperthermia
frostbite