My 13-year-old cat is meowing loudly and hiding. What's wrong?

Thanks for using Petco Pet Education Center, formerly Petcoach! A few main concerns are coming to mind for Bubbles.

1) Hyperthyroid disease- the vocalizing fits with this but usually an increase in appetite is noted. We also usually see weight loss. This can be diagnosed with a blood test that may or may not be a part of the "regular" bloodwork done.

2) Pain - a severe arthritis flare up can cause vocalizing and reluctance to move. If bloodwork comes back normal, x-rays and or a pain medication trial would be my next steps.

3) Cognitive dysfunction (senility) or other neurological problem - Though it is not as well documented in cats as in dogs, we do definitely see cats that have dementia. This usually manifests as: wakefulness/vocalizing at night, loss of litterbox training, seeming to be lost, sudden anxiety, and other signs.

I have seen cats act like this with sudden blindness (a few underlying causes) because they are anxious to leave the places they know best (bed, food, litter box).

Finally, brain tumors, clots in the brain (underlying heart disease) and other neurological problems may manifest similarly to this.

Long story short, get a good eye exam and some bloodwork done. Then consider x-rays and/or a pain medication trial. If none of these help, discuss possible next steps with your vet.

Best wishes to you and Bubbles!