I agree with the others about it could be a passing injury. That happened to Sunny when she jumped down off the fence and hurt her shoulder, and was growling and holding her paw up, we rushed her to the emergency vet (it was a weekend) and he gave her a pain kiling injection then charged us £75.00! (which I think is about $145??ish) cause it was out of hours.
Then when we got home she run up the stairs jumped on the bed and went to sleep with no problem at all! I could've killed her, lol!
So it may be that it will wear off after he's rested.
Animals are knowledgable when it comes to hurting/injuring themselves, they always know they have to rest so it will get better.
Get well soon Chowder!