General Symptoms

• A sick cat may exhibit physical signs as lethargy or weakness, weight loss, vomiting or diarrhea, difficulty walking, coughing or sneezing, open-mouth breathing, or seizures. Increased scratching, biting or licking may also provide a clue to a cat's discomfort. Sudden personality changes like increased irritability or hyperactivity may also be noticed. Since each cat responds to illness differently, owners should watch for any behavior that seems out of the ordinary.
  
  

Eating and Drinking Behavior

• While a cat's lack of appetite or thirst is a common indicator that something is wrong, some medical conditions can lead a cat to eat or drink more than usual. Therefore, any changes in a cat's normal patterns should be carefully scrutinized.
  
  

Litter-Box Behavior

• A healthy cat's litter-box habits are fairly consistent. Such changes as increased frequency of trips to the box, straining or crying out while urinating or defecating, or eliminating in places outside of the box are typical warning signs of illness.