The doctor was gentle and calm with him, and Chimera handled it really well. He mostly hung out on my lap during the adjustment and was relaxed. There were just a couple of moments when he lip licked or turned his head away as stress signals. I was pleasantly surprised by how well he handled this new, strange situation. All the handling work I've been doing is paying off!
The doctor said that he did have a disc out of alignment. He also said that I could retry the collar grabs after a couple of days and see whether the adjustment fixed the problem. However I think that I'll just avoid them completely. We've been making very good progress with the weaves, and everything else, without it.