Turns out they found spinal stenosis. There's no cure, no treatment to speak of, beyond palliative care. Currently, I have to give him strict crate-rest for 4 to 6 weeks—even after he seems to be getting better.
He's 11, but he's not an old dog; I mean, he seems older than he is because he has such difficulty walking. (I was plan nasty to a woman this morning who cocked her head and smiled before asking, "Is he an old dog?" "Leave me alone!" I bellowed. I was in no mood for chit-chat.)
I usually have to carry him; I have to carry him both up and down all five flights of stairs in my building—which I'm resigned to. You do what you can for the ones you love.
I'd like to get him a photonic-therapy unit—and now that there's a distributor in this country, I may do that; when I last checked, the only contact in the whole world was an address in Australia. When I mentioned it to the vet I saw last week, she thought it was a tall order for me to go learning all the acupuncture points, but I think it would be on an as-needed basis.
Unfortunately, he pooped in the front hall of the building earlier when I was carrying him out—and I didn't notice. Carmen—the woman in the front apartment, who's the de facto super and package receiver for the building—wrote a misspelled note and taped it to the glass of the front door about how tenants weren't supposed to let their dogs poop in the hallway without cleaning it up. Most tenants don't have to carry their dogs both ways.