Okay, update.
I did call the 24 hour emergency vet, and sure enough, they wanted me to bring him in. They asked a bunch of questions, notably if he was panting–he wasn’t–and said Hmm, could be a number of things, better bring him in.
Now at this point, he didn’t want me to even touch him, let alone move him. So I thought possibly I could slide him onto the carpeted board that goes in the bottom of the cat carrier. As soon as I touched the cat carrier, he managed to get himself off the chair and hide.
So I put the carrier back. About a half hour later he came back to my office and back to the chair, slowly. He got back into the chair. At this point he was moving slowly, but he let me touch him without complaint. I went over him looking for tender spots, a stinger, a welt (not that I could feel a welt under all that fur), and found nothing. But he seemed perfectly comfortable in the chair, so I left him there. Left notes for people who get up earlier concerning his condition, and went to bed.
This morning, he was still not quite moving up to par, but he wanted out. We did not let him out. About mid-day, he did go out and jumped into the hammock with my husband. At this point he seems perfectly normal. Not as active as usual, but it’s a hot day.
Now, as to why I didn’t take him to the vet. One, he had seemed perfectly normal, curled up on the chair, until my son tried to pick him up, and at that point he didn’t want to be touched and he REALLY didn’t want to be picked up, but he seemed perfectly happy to be curled up in the chair. He did have some difficulty changing his position. If he had some internal injury, I really wouldn’t want to risk moving him and hurting him worse. Two, when he’s been really hurt–beat up from a fight, and with a fever, and really feeling bad–he has hidden. But in this case he didn’t hide, and was in his usual place, which is almost always close to one of us, and he didn’t hide until he saw me getting the cat carrier.
If he had been too sick to protest when I got the carrier down, THAT would have really tipped me off that he was in bad shape.
Also, when he fell over, he briefly did that cat thing (“I meant to do that, just let me lick this paw here, then I’ll be right along”) so, while the falling over freaked me out, the recovery gave me hope.
And he seems to be doing fine today, as I said. I guess he is officially a medical mystery now. I have no idea what happened. It was a hot day yesterday but if he had some kind of cat heat stroke, it seems odd that it would happen late at night, after it cooled down.
(The last time I had to haul him into the emergency vet was during a snowstorm so bad that my office was closed and my regular vet was closed. I got the car stuck, with a howling cat sitting in a carrier beside me. Some Russians pushed me out and joked that I had my own siren.)