Is it hypo or hyperT? Hypo is pretty rare, I think?
Has Gary been to the vet for a recheck since he started treatment? I'd recommend a vet visit, as there's very often a medical issue underlying sudden behavioral changes, especially in senior kitties. If he's only yowling at night, when you're asleep, it suggests that he needs your reassurance because he's not feeling well, or maybe because his vision or hearing is starting to fail. Have you noticed any hesitation before he jumps up, or especially before he jumps down?
I know what you mean. I had a kitty who was blind for the last 5 or 6 years of her life, and I would get frustrated with her sometimes. Of course it wasn't her fault that she couldn't see and wanted constant reassurance from me - in fact, it was mine, because I could have prevented her blindness if I'd been more knowledgeable - but it was frustrating all the same.
I hope you're able to figure out what's going on and get some sleep!