It happens more often than you realize. You’re drifting off into sleep, but suddenly, you feel an unexplained chill. You grab for another blanket, pull your hoodie tighter or tuck your feet in deeper.

Feb. 12, 2002 — -- Most have felt the chill of a winter wind, the dull sting of poking a toe in icy water or the cool taste of a cough drop. But until recently, scientists haven't really ...