As you know, hypothermia is a temperature related disorder. Therefore, it is necessary to understand human physiology as it pertains to temperature stress.
Man is considered to be a tropical animal.
Comfortable human survival using only that protection from temperature stress which is provided physiologically at birth would therefore require an environment providing a temperature of 37 degrees Celcius, plus or minus perhaps 1 degree. The response to an upward variation in body temperature is the initiation of perspiration, which moves moisture from body tissues to the body surface. When the moisture reaches the surface it evaporates, carrying with it a quantity of heat. The explanation for a person becoming thirsty when exposed to a hot environment for a period of time is that fluids lost due to perspiration must be replaced. The response to a downward variation in body temperature is shivering, which is the body's attempt to generate heat.