Hi,
I have an 11 year old cat who has , over the past few weeks, become more withdrawn and just acting.. different. He doesn't come when he's called, he kind of hides from everyone and the other cats (one his brother and one his best friend). He just has lost the spring in his step and even his body stance is different. His eating habits and everything are the same. I'm not sure what it could be. I know I need to take him to the vet, just kind of dragging my heels. Thought I'd check here first.

Any replies would be appreciated.

For a cat that age, I'd recommend taking him to the vet. It is common for them to start having thyroid problems when they get older, so that would be a good thing to check. Keep an eye on his eating and drinking behaviors, and his weight. Weight loss is a big sign of thyroid disease.
He may just be slowing down in his old age, but it's always a good idea to do a geriatric checkup and get baseline values on bloodwork, urine levels, and glucose levels (they can get diabetes like humans, also).
Hope all is well.

Hello,

Make sure your cat is urinating and stooling appropriately. Cats can become blocked (esp. males) and/or constipated. If either of these occur, it is an emergency situation and needs to be seen immediately.

Is your cat obese? Has there been some change in the household (a death, someone moving in or out, workmen, etc.)? What kind of food is your cat eating? Has this cat always been the shy/easily stressed type?

I agree with Tiger that some labwork is in order but don't ignore any external stressors that might be causing issues or behavioral changes.

If you are not already, think about feeding a high quality diet for older cats such as Iams Hairball or Hill's Advance Protection Senior.

Please don't drag your feet on this. By the time a cat starts showing signs of illness, it can almost be too late.

Keep us advised of your cat's health.

Regards,