Hi, I recently bought a new brand of food for my cat and like always started mixing it in with the remaining old food so he'll be used to it. Just about 3 weeks ago I went out of town for a day and came back to find that he had vomited what looks the semi-digested food. Last night almost 3 weeks later he vomited again, but there was less. Should I be worried about this and if so what should I do about this?