His blood work came back... essentially normal. :-/ He has kidney disease but his levels hadn't changed since his last workup in August. Doesn't have diabetes. I talked to my vet about the fact that aside from his appetite, which has improved significantly, his symptoms seem to be neurological. She noted that they hadn't taken his blood pressure... so it was off to the vet again tonight. Where they found that his BP wasn't high enough that it ought to have been a problem. She checked out his eyes... no retinal hemorrhages, nothing that would clue her in to a blood clot problem or stroke. She could see that he was moving a little wonky on the slippery floor, but they played a game where the vet tech chucked treats around the room so he had to go get them, and he didn't do anything particularly worrisome. So the basic plan right now: watch him, and feed him whatever he'll eat.
Right now he's lying behind me in the computer chair, doubtless using my ample posterior* as a hot water bottle. (* Basically since Mom got hurt, my gym attendance has diminished to nearly nothing and my eating habits have gone to hell. Bad combination.)
Not quite ready to comment on the night's big news, but it sure looks good from where I sit!