Poor Ozzy! Have you checked his temperature? If his temperature is normal, and his general condition is OK, then I wouldn't worry yet. We've all had upset tummy, and it usually gets better by itself. Don't give him any food for 24 hours, then start him carefully on foods that are easily digested. Overcooked chicken and rice for instance, maybe with some yogurt (the type without flavour) to stabilize the stomach. The drinking is the important part, making sure he gets enough fluid. You could mix some yogurt into the water to make it more tempting, or if you boil some chicken use some of the water from that to add taste and smell. Hope he feels better soon!