Does he do the "scarf and barf", i.e., he gulps his food down and then up it comes? One of my cats does that and sometimes she doesn't even leave the food dish, it comes up that fast. She'll only eat dry food, hates canned, so I scatter her food on the floor which makes her slow down and not gulp it. If that isn't the case w/your cat, though, it might be a good idea to get a second opinion. If your instincts are telling you that something is wrong, have it checked out.