Changes in Behavior
Cats who are injured or sick may act differently than they normally do. Friendly cats who usually love to be around people might start to hide from them, and energetic cats might become lethargic. You might also see their normally fastidious grooming habits fall by the wayside. You should know your cat better than anyone else, so make an appointment with your vet if you see any obvious behavioral changes.
Changes in Appetite
Cats tend to refuse food when they aren’t feeling well, but some illnesses can actually make them hungrier. Other illnesses might also make your cat thirstier. Cats don’t actually need to drink that much water since they are descended from desert animals, so suddenly drinking a lot of water is usually a sign that your cat might be sick.
Discolored Gums
A healthy cat’s gums will be pink, and discolorations are indicators of an illness. Yellowish gums are an indicator of liver disease, while bluish gums could mean an unhealthy lack of oxygen. In short, if you have the chance to look at your cat’s gums and they aren’t pink, you should be calling a vet.
Repeated Vomiting
All cats vomit on occasion if they eat something disagreeable or if they’re nervous, but repeated vomiting is a sign that there is something wrong. Contact your veterinarian if your cat vomits almost every time it eats, if there is blood in the vomit, or if the vomiting is accompanied by lethargy.
Source:
http://www.adventurecats.org/gear-safety/8-signs-your-cat-needs-to-go-to-the-vet/
