I took him to the veterinary hospital this morning.
They think there may be some kind of neurological damage, like possibly a brain lesion.
They're keeping him there overnight.
Tomorrow they'll know more about what's going on.
There are a few things they need to do to determine the source of the problem.
They gave him sedatives so he could relax and stop the compulsive circling.
They gave him some other things too, and said his response will help them narrow down what's going on.
Their hope is that when the sedatives wear off, his brain will sort of "reset" itself. Apparently it's worked before with other cats in this situation. Sometimes. Not all times.
When I stopped in to visit him later this afternoon, he was completely sedated. Poor thing. He was there in his little assigned area, asleep but looking extremely worn out. I had to look closely to make sure he was still breathing.
They said as soon as the sedatives relaxed him, the first thing he did was pee, since the compulsive circling behavior had been making it impossible until then. (He hadn't been able to stand still or stay in one place long enough to go to the bathroom. It's like all his brain wanted to do was move in circles over and over and over and over and over. He'd keep moving in circles until he was so exhausted he couldn't move anymore. He'd crouch down in an odd crumpled sort of way until he'd regained enough strength to start circling again. Over and over and over. Disturbing and sad! Tuesday night I held him for three hours, just to keep him still. He purred at 10:00pm, and after that he wouldn't purr anymore. He just looked and sounded miserable.)
Depending on what ends up being wrong, they might be able to save him.
And it remains a distinct possibility that he might not be save-able.
They said that even if he recovers, he will never be exactly like he was.