I don't know about cats, but elderly dogs can get CDS (cognitive disorder syndrome) which is basically doggie Altzimers. Vets say they are seeinfg more of it because dogs are living well into old age due to better care, food etc. I had a little doxie that got it when she was around 15. She got really bad over a period of 6 months or so. I finally had to let her go, she had no quality of life.