you can see if he wants some crushed ice if you have some or offer him a little water in your hand even...i wouldn't worry until tomorrow too much.

it takes some dogs a while to really come out of the anesthesia...if you vet is still open you can call them & talk to them just to ease your fears...chances are tho he is hurting some & his stomach is still upset some & just doesn't feel like moving, drinking etc. my tomorrow you should be back to normal...if not call them for sure.