According to the Search and Rescue Association of British Columbia:

"Man is considered to be a tropical animal. Normal functioning ... requires a body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit)... plus or minus perhaps 1 degree.

The response to a downward variation in body temperature is shivering, which is the body's attempt to generate heat. ... This muscle action creates heat through friction. Hypothermia is defined as a core temperature of less than 35 degrees Celsius. "

If you didn’t catch the math, that’s a drop of only two degrees from normal!

Many variables contribute to the development of hypothermia. Age, health, nutrition, body size, exhaustion, exposure, duration of exposure, wind, temperature, wetness, medication and intoxicants may decrease heat production, increase heat loss, or interfere with thermostability.

Ok, so what are the signs of Impending Hypothermia?

Core temperature has decreased to 36 degrees Celsius. The person will increase activity in an attempt to warm up. The skin may become pale, numb and waxy. Muscles become tense, shivering may begin but can be overcome by activity. Fatigue and signs of weakness begin to show.

For many of us, this sounds familiar, doesn’t it? A little Mild Hypothermia doesn’t seem that bad:

"The core temperature has dropped to 35 - 34 degrees Celsius. Uncontrolled, intense shivering begins. The victim is still alert and able to help self, however movements become less coordinated and the coldness is creating some pain and discomfort.

But this is a warning—by the time you start feeling this way, you should pull off the road and do something about your condition, or it can worsen:

Core temperature has now dropped to 33 - 31 degrees Celsius. Shivering slows or stops, muscles begin to stiffen and mental confusion and apathy sets in... breathing becomes slower and shallow, and drowsiness and strange behavior may occur."