A sudden decrease or increase in appetite can be a sign of illness.
If your cat is normally active but suddenly becomes lethargic, this could be a sign of illness.
Vomiting and diarrhea are common signs of illness in cats.
Increased thirst or urination can be a sign of kidney disease or diabetes.
Difficulty breathing can be a sign of respiratory infection or heart disease.
Coughing and sneezing can be signs of respiratory infection.
Changes in behavior, such as hiding, aggression, or vocalization, can also be signs of illness.