Many thanks for the good wishes and thoughts for my BoyCat!
He's doing better today. He was transferred from the emergency clinic to the 24-hour vet specialty clinic this morning, where a cardiologist examined him and diagnosed him with restrictive cardiomyopathy. Cause is unknown, but it's likely that the heart disease had been progressing for some time and the stress of the abscess treatment sent him over the edge into heart failure.
The prognosis is a bit better than it was last night: six to eight months if he can be successfully weaned off of oxygen and responds to the heart meds they're starting him on today. The vet hopes he'll be able to come home tomorrow afternoon or evening. I'm keeping my fingers crossed.
He doesn't appear to have any neurological damage from the heart failure, which was a real possibility because his pulse-ox was very low for a while. He clearly knows me, and he was very affectionate to me during the drive from one clinic to the other this morning and again when I got to visit with him for a few minutes at the 24-hour clinic before they shooed me out. They opened a small window in the oxygen tent for me to stick my hand in and pet him, and he immediately crammed his head and front paws through and tried to climb out--either to escape or to sit in my lap.
I'll get to visit him again tonight for a few minutes. Can't wait to bring him home!