Ever notice that when you're all bundled up (probably in several layers!!) and head out into the cold you're hit with the urge to pee? Turns out it's not all in your head.

It's called cold diuresis.

There's a rather dry (no pun intended) medical study from about 60 years ago that explains the phenomenon, but here's the short answer from OutsideOnline.com:

When your temperature starts to drop, your body will attempt to reduce heat loss by constricting blood vessels and reducing blood flow to the surface of the skin. When that happens, your blood pressure will rise, because the same volume of blood is flowing through less space in your body. In response, your kidneys will pull out excess fluid to reduce your blood pressure, making you have to pee. A full bladder is a place for additional heat loss, so urinating will help conserve heat.

And you thought it was just your imagination!