Since cats can’t talk and tell you if they’re feeling bad, you have to read their body language and their behavior. Then hope you’re deciphering their body language and behavior correctly so you can make sure your cat is happy and healthy.
One sign of a content cat is whether it grooms itself. Since cats can keep themselves clean, any sign that a cat isn’t grooming itself is a sign that something could be wrong.
Also look for signs of social interactivity. Cats are social creatures but if they change their habits, that could be a sign of problems or just a sign that your cat is messing with your mind.