crisper, please take him to the vet, if only to set your mind at rest. Our Rover was doing that two years ago - he was really hungry and ate all his food, then a few minutes later chucked it up again undigested. Blood tests showed that he had kidney failure (which is common in cats) and that the bile in his stomach was making him vomit. He was very easily treated with some rehydration and then a daily tablet of Fortekor - at the time he went missing, he was healthy and strong, and his blood results were as good as a well cat. Rover didn't appear to be in pain, just very hungry, and was getting dehydrated because cats get so much of their liquid from their food. Please take your boy for a blood test - just in case. they can do so much these days for cats with kidney problems.