I'm glad you already have a vet appointment to get him checked out! Never a bad idea.
What temperature is his cage? Do you have a heating set up for him? Does he get 12-14 hours of light during the day? It sounds a bit like a possible hibernation attempt to me, which is why I'm asking.
What kind of wheel does he have? I know I found that Comfort Wheels were prone to falling over, especially if you used liners instead of a loose bedding that you can bury the wire in. Attaching it to the cage wall with a metal clip (like on a dog leash) might help keep that from happening again, just in case.
~*~*~ Kelsey ~*~*~
RIP my sweet Lily ~ 6/12/08 - 1/20/12