I can't tell what is causing him to do this since the symptoms are not specific of any single illness. However, with the vocalization, and the dilated eyes, several possibilities comes to mind:
.usually a urinary blockage they try to urinate, maybe that is what is doing when he is hiding.
.abdominal pain: so many conditions, not possible to list them all
. other painful situation.
-Diabetes/kidney disease: have you noticed an increase in water intake, urination in the last few weeks, months?
-Heart disease: sometimes no prior symptoms. Cats can develop a thick heart muscle (hypertrophic cardiomyopathy), this will cause less blood to be pumped at each heart beat, so the heart muscle needs to compensate.
- FIE: feline ischemic encephalopathy. This is a vessel spasm not a stroke.
-Dilated eyes, acting blind. Hypertension (retinal detachments) from kidney insufficiency/failure. cancer, auto-immune disorder, infectious (less likely if not going outdoors, and not other new kittys in the household, not hunting, or not eating raw food), coagulation disorder.
Unfortunately a lot of conditions are possible. A good physical examination will include the heart/lung auscultation, eye examination with an ophtalmoscop to check the retinas, an abdominal palpation ( may help detect constipation, an abnormal bladder, etc). depending of the physical examination, the veterinarian may discuss treatments and/or diagnostic tests.
I would recommend you seek veterinary care today, since we do not know the origin of the problem. Since some of those problems are life threatening, I would not wait.
Let me know if you have more questions, or need additional information.
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