Hmmmmm....well, it could be any number of things. Did you change the setup at all? Put any new hides in? Change what was fed? It could be that he is just fussy because he was cold.

But like I mentioned, it's definitely good that you're taking him to the vet. Even if nothing is wrong, it still is a good precausion and will ease your mind (or let you know what is wrong).

Good luck!!!