When I go to bed, I typically wear a T-shirt and underwear and have a thin comforter over me--I feel completely fine before falling asleep initially. Then what happens is I'll wake up in the middle of the night and be absolutely burning up. I'll be sweaty and uncomfortable and have to take my shirt off and often that isn't even enough. It makes little sense to me, especially as the temperature in the room has dropped by then. And often when I go back to sleep and wake up again in the late morning, I'll be cold from having taken my shirt off. What's with the changes?