Turn on the heater, lol! It is pretty standard, besides i read somewheres that we need to get the direct sunlight for vitamin replenishment and apparently in winter its much harder to get.
So stop, think about some good things in winter to do... i personally, prefer a warm drink (be it corny...like coco or harder like scotch). Download a few movies and cozy up under a blanket or read or something.
Personally, everyone hibernates in winter. It's a necessity in my eyes.