Increased Water Consumption :
Drinking more water is associated with a few diseases including kidney disease and diabetes mellitus. If you notice your cat is showing these symptoms, see your veterinarian.

Not Grooming :
Cats that don't feel well don't groom. Sometimes this is the first sign of illness some cat owners will notice. The hair coat is matted or just not being kept as clean. If your cat is not grooming like they used to, have him or her evaluated by your veterinarian.

Bad Breath :
Bad breath, also known as halitosis, can result from dental disease as well as other metabolic disorders.

Inappropriate Elimination :
Most often inappropriate elimination involves urinating outside of the litter box. This can be a behavioural disorder as well as due to a variety of urinary tract diseases. Have your cat checked by your vet to determine if there is an underlying cause for this behavior.

Sleeping More :
Sleeping more can be associated with lethargy. Cats sleep an average of 13 to 16 hours each day depending on the age and personality of the individual cat. If you notice your cat is sleeping a lot more than he used to, don't assume it is just age. Make sure that is not an underlying disease or illness.

Less Involved In Social Interaction With You Or Other Cats :
Cats that don't feel well, don't tend to play or be as social with you or your other cats.

Drooling :
Drooling or hyper salivation can be associated with oral or dental disease and should be evaluated by your veterinarian.

Vomiting :
Gagging or vomiting is a very common sign of illness. Some cats will vomit occasionally or vomit a hairball. Vomiting that occurs once a week or less frequently is generally not a problem. However, if your cat is vomiting on a regular basis or is losing weight, this could be an indication of a serious problem.

Difficulty Breathing :
This is a very severe sign of illness. It can be caused by underlying heart or lung disorders as well as anaemia. Difficulty breathing can be noted as increased respiratory rate or effort, open mouth breathing, or a posture in which the arms are slightly abducted and your cat neck is extended. This is a life-threatening emergency.

Diarrhoea :
Loose stools can be caused by dietary reasons, allergies and other gastrointestinal diseases.

Coughing :
Coughing is relatively uncommon symptom in cats but is serious when it occurs.

Bloody Urine :
This can be a sign of urinary tract disease or infection in cats. It should be evaluated immediately. It can also be associated with urinating out side of the box or frequently attempts to urinate.