Oscar update. TL:DR - He survived his harrowing ordeal. THANK YOU all for the positive vibes!!!
I've known since he was a kitten that he has a liver shunt, a bad heart and low-functioning kidneys. Most vets wouldn't listen to me but I finally found one local who determined that I probably knew what was wrong - hepatic encephalopathy. He was completely unresponsive save for involuntary muscle spasms, breathing fast and hard, had his jaws clenched and couldn't swallow. She just gave me a bunch of medications and an IV and told me good luck. She said she expected him to not survive the episode. That was two years ago.
Rushed him to the vet Friday with the same issue - catatonic, drooling uncontrollably, and arching his neck and head back. The vet took one look at him (different one) and said she was so sorry but she felt he was trying to die. His core temp was 92 when it should have been 100. I was crying but I told her to please hear me out and give me these things I needed. She said she wouldn't even question my request, gave me the stuff, hugged me and said she was sorry. I told her I'd be calling her in a couple days to prove her wrong.
Today, Osk is still somewhat wobbly but he's been mewing softly from his mobile medical cart, he's eating small bits of food and drinking really well. I'm still giving him sub q fluids regularly and he's enjoying baby food and ricotta cheese.