Male cat is almost 10 y/o and has gone from 12 lbs to 7. Blood work, x-rays, and ultrasound only shows 1 kidney 10% larger than the other (vet said this wasn’t an issue) and a slight heart murmur. Gave Royal Canjn recovery but after a few days he stopped eating that so back to his regular food. His behavioral changes are minor… sometimes acting more affectionate and once in awhile hissing at the other cats (which he didn’t do before). His energy level hasn’t changed, but every now and then he will just stare into a corner or at a closed door until you call his name and he then acts as if it was nothing. After searching on the internet I’m wondering if it could be Feline Cognitive Dysfunction Syndrome but vet didn’t mention that. Could that be it, or is there something else the vet and I are missing?