I get really cold after my workouts, too, but it's not hypothermia. If anything, your temperature is elevated. Think about it, if you have a fever, you'll feel cold. Of course, elevated temperature post-workout is *not* a fever.

It is known that the body "reacts" to exercise for several hours after. I think what you're experiencing is actually quite normal. Apparently, there are NOT enough PhD candidates conducting studies on this issue.