Lydia got knocked down by a Snow Bear, I killed it, now she just crawls around everywhere I go as though she's still injured. I tried to heal her and she's at full health, I tried attacking her and she keeps crawling around... I dunno, guess i try and get her back into combat.

Tell her to return to the house if you can.

I fast traveled and it fixed it. I was going in and out of doors at winter hold and it didn't fix it, guess fast travel works. Beware.

I had this same problem with the guy who accompanies you on the first Companions quest - he was crawling along on his hands and knees. I got fed up and left him behind after a while, but when I made an area transition somewhere (probably to another level of the dungeon) he was magically upright again.

When this happened with my companion all I had to do was re-enter and leave stealth while standing near them, then they stood up.