What is cold?

I always learned, according the basic laws of physics, that cold is simply the absence of heat. That there's no such thing as "cold" as an entity in and of itself. Well, last night my feet -- yes, my feet -- proved me wrong.

I have really poor circulation, to the extent that it is not unusual for my entire body to be perfectly warm and my feet (and/or hands) to be icy. (Of course, sometimes those appendages feel like they're burning up when the rest of me is comfortable...but that's off the topic.) Last night, I couldn't get my feet warm by encasing them in socks and blankets, which often happens because the layers just act as insulation to keep them as cold as they already are. So I went into the kitchen where there's a hot-water pipe running floor to ceiling and pressed my feet against it, in my socks, until they were truly toasty. I then went back to bed, under my down quilt, still wearing the warmed socks. Within five minutes my feet were cold again. Tell me, please, how it is possible that my feet generate cold???

Oh...and it serves me right that the night after posting that I rarely ever have trouble falling asleep, I should have lain in bed awake for about an hour and a half in total. The stress of my upcoming move is getting to me.