Could your cat be sick? It may be difficult to know if subtle changes in your cat indicate a health problem. Cats are experts at hiding illness. In the wild, this instinct can protect them from predators or other cats that might be a threat. Today's house cat has the same tendency to avoid vulnerability, even if the only potential threat is a housemate. Even cats in single-pet homes tend to have the instinct to self-protect.
By the time you actually notice something is wrong with your cat, it might have been going on for a longer amount of time than you think. Note subtle changes in behavior and watch for more. Observe your cat's demeanor and body language. Does something seem off? That's when you can actually conclude if your cat is sick or not.
Never ignore obvious signs of illness. When in doubt, contact your vet for advice. Vomiting is not normal in cats. Some people think it's ok for a cat to vomit every few days, but it's not. Things like rare vomiting or the occasional hairball are not concerns. However, anything more than this warrants a trip to the veterinarian.
Diarrhea may indicate dietary indiscretion, intestinal parasites, and a variety of other problems. Left untreated, diarrhea can lead to dehydration and further intestinal inflammation. It's also very uncomfortable for your cat. Schedule a vet appointment and, if possible, bring a stool sample.
Loss of appetite can be normal for cats but it still should not be ignored. If your cat skips the occasional meal but otherwise eats normally, then you should watch closely for trends. If your cat stops eating entirely or is only eating tiny amounts, you need to get your veterinarian involved. Lack of eating for even a few days can lead to a serious problem called fatty liver or hepatic lipidosis.
Increased appetite may also be a concern, especially if it comes on suddenly in an older cat. Hypothyroidism may be the explanation, but your vet will need to run tests to be sure. Increased appetite should not be ignored, even in younger cats. If nothing else, it can lead to overeating and obesity.