Okay, here is where we are at:
Came home, Dante was alive and awake and laying quietly on the bathroom floor. I immediately gave him his hugs and brought him out to the living room and force fed him about 10ccs of water. Then about 5ccs of pureed food. Upon examining him, his coat is healthy and shiny, his eyes are clear and no inner eyelid visible, temperature normal, breathing normal, heartbeat normal. It even appeared that he had been drinking water during the day because he was already hydrated (skin pinch test).
I was on the phone, texting Bluce, no less, and I watched as he got up off the floor, walked to the litterbox and PEED! It was normal pee, not dark or reddish (indicating blood). He came out and laid down, and I was stroking him and his rear flank and I felt a mass. The poor guy is clogged up, and that is what is causing this shit. When he walked to the litterbox, he did not wobble or fall down, but was obviously weak on his legs. Again, not unusual with constipation, even in humans!.
I have changed his vet appt to 740am tomorrow morning, and he will get an enema and whatever he needs to clean him out. Once that is done, his energy levels and movement should return to normal. Even if diagnosed with megacolon (severely distended colon caused by repeated constipation), he will survive and still get his back legs to normal. However, no more free feeding. No more dry kibble. It dries overweight cats out. I will have to closely control feedings, and have him only eat the wet food.
He will make it through the night for sure.
And I am confident that he will be back to normal very soon and I will not have to think about the unthinkable. I don't know any of what is wrong for sure, but I think I have it nailed. For now, I will relax and keep him near me and force water but not food. He is next to me right now.