Is my older cat in pain?

You have previously mentioned that cats are adept at hiding illness and particularly pain.

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I have an 11-year-old cat and I would like to know if there are any pointers to a cat being under the weather, or in pain?Some of the more serious illnesses are obvious, usually with a complete loss of appetite or signs such as difficulty in eating, loss in weight, sneezing, coughing and runny eyes, for example.