What does my cat's behavioral change indicate?

My usually sociable female cat has retreated under the bed in the guest room. She will come out but seems distant.

She is drinking water but not eating much and, when I stroke her, she purrs but then makes a smacking sound with her mouth, as though she's tasting something unpleasant. Why?

Editor's note: I would make a trip to the vet a priority. One of the first things a cat does when illness sets in is go off food, and often may become more aloof.

Behavioral changes, such as going from being sociable to aloof, or sleeping more are often a sign of ill health.

I failed to notice this change in Priscilla one time, and I'd never make that mistake again. She was diagnosed with an infection of unknown origin. In the end, she was fine, but not until after injections of subcutaneous fluids, some medication, and some rest.

I hope she recovers quickly.
-Kurt