If your cat displays any of these symptoms it is worth going to see your local vet as soon as you can. It is better to be safe than sorry:
1) Weight loss. Although one is not expected to weigh one's cat everyday, a cat will often lose a significant amount of weight if it is unwell. Without whipping out the scales the best way to tell if your car has lost weight is: firstly to pick her up-does she feel lighter than usual? Secondly to smooth her fur, are parts of her that used to be well rounded now flat? Of course at this juncture it is important to point out that during the summer months a cat will shed its winter fur so please account for this in your weight loss estimations.
2) Linked closely with #1, has your cat lost its appetite? Like humans a loss of appetite might be due to either unpleasant reaction to food, like vomiting, or a more serious problem that may stop a cats stomach from being able to feel hunger. Measuring a loss of appetite is not as easy as it sounds. Taking my own cat as an example, he has little periods of liking certain foods and then going off them without a moment's hesitation (usually after I have stocked up on the bumper pack!). So please factor this into your thinking. It would be terrible to force a cat off to the vet only to uncover that your cat has decided that the food you have been buying for the past five years is no longer what she wants. My recommendation is to try a different food brand for a day or two, and if then there are no improvements then a trip to the vets is unavoidable.
3) Change of behaviour. A sure sign that your cat is ill or possibly unwell is a sudden change of behaviour. If your cat is usually an outdoor cat, yet for the past few days you have found him hidden under the table unwilling to move, then you may well have an unwell cat on your hands. A further noticeable behaviour shift is linked to your cat's general movement. If your cat is usually jumping up on your lap, the furniture, and indeed any object that takes his fancy yet recently hasn't felt comfortable doing so for the last few days, you cat may be ill. Cats are traditionally routine animals, and any break from this that has not be caused by a change of routine from you, can indicate an illness that might be hidden from view (i.e. no loss of weight or appetite) but may indicate internal problems that require urgent vet attention.
John Sanderson is a keen cat lover who has recently written a 5 day mini course on cat training. Did you know that there are 5 foods that you must not feed your cat? To find out what they are and more please go to Cat training Secrets