My cat Yoda is almost 19. She's an indoor cat who has been pretty healthy her whole life. She's always had issues with vomiting if she has dairy or cleans herself too much. She normally has diarrhea now, even though she normally has fish or chicken and maybe some dry food as her only meals. However, she is as healthy as you could expect from a cat that old.
The last few days she has eaten less and laid down on a spot in the kitchen where she never lays down. She usually loves to lay on me but hasn't interested in doing that for the last few days, she seems to like cooler surfaces, like the top of a trunk or tile floor. It seemed like she was just changing her normal routine, which she sometimes does, but today she hasn't eaten or drank or slept at all. We gave her water with an eye dropper but she threw that up a few hours later. She doesn't lay down or walk like normal, but doesn't appear injured.
We don't have a lot of money for a vet, will probably take her tomorrow.