Our cat is 13 also, and for the past 2 months she was throwing up a lot and generally acting like something was wrong. Her vet did bloodwork, an x-ray, and 2 exams over the past 2 months and everything came back normal. Finally last Fri. they put her under anesthesia to examine her and it turned out that she had a torn ACL in her right leg! She had surgery on Mon. to repair it and although she's laid up right now, she's back to herself. Do you think that your cat might have an orthopedic injury? It was *so* subtle...you could see that our cat was "off" and that her gait was slightly strange. Even the vet couldn't tell during a routine exam.