If you started a new bag of food or switch between varieties, could be that.
Otherwise, a temporary illness, if not something he ate, could be a virus... and based on his recent extended trip to the vet, I would wonder if he might have picked it up there, as well as being a bit more susceptible due to the stress of surgery?? Cats do get illnesses, just like people, that are not vaccinated against, but not as often. Just a guess, though!
Hope all's well from here.
Last edited by SamIam; March 21st, 2011 at 02:53 PM.