Vet says "put him down;" Need your advice

I rescued a cat from the streets this past winter, about 2 months ago. A week ago, I suddenly discovered a wound on his cheek. I thought he had scratched himself open. I did notice a short time earlier that he had an ear problem when I saw him shake his head, and I could tell that his ear was bothering him. Anyway, when I investigated the wound, I discovered that he had developed an abscess. I took him to the vet, and they fixed him for a whopping $750. They also advised me that he might have rabies. I took him home and, a week later (last night), I suddenly noticed his eyes were hugely dilated. Just then, he ran to the bathroom (his box) and vomited and defecated involuntarily. Worst yet, he then collapsed into the vomit and feces. I picked him up and put him in the bathtub. He lay there for an hour, splayed out. His legs were in an obviously uncomfortable position, but he could not move at all. His breathing became rapid and shallow. I thought he was dying right in front of me. After an hour, I picked him up and put him in a chair. He lay there for 3 hours. I went to sleep. When I awoke at 4 in the morning, he had gotten out of the chair and was trying to walk. It looked like he was trying to walk off something. He did this for 3 more hours. He would walk from one end of the room to the other, pausing to stare at the wall and then turning around to do the same thing on the other side of the room. When the vet opened at 8 AM, I took him right in. They said he may have been convulsing due to rabies. They suggested I put him down. I don't want to. I've decided to go for the rabies shots for myself (because he did scratch me once while we were playing) and wait to see how he develops. Does anyone have an opinion what might have happened to him? Please?

They've kept him. He's still at the hospital. Thanks for replying.

They are waiting to see if it happens again so they can witness it. But they said he was back to normal and eating. The problem is, if they put him him to sleep, they're going to test him. And then, if they come back and say he was negative for rabies, I am going to feel very, very bad. This animal really loves me. I feel I've got to hold out hope for him. I know he was suffering last night, but he's not suffering now. We're just waiting to see if he does it again. I would appreciate everybody's opinion.

The only way to test for rabies is to send a slice of brain tissue off to the lab. So they have to put him down to do that.

His name is Charlie. I just called the vet for the morning update. She wasn't available, so I spoke with the tech instead. Charlie is behaving normally. If he had rabies, since it progresses quickly after onset, the appearance of other symptoms would be expected within a day or two. This is day one after the episode. He's not showing other symptoms. I'm going to go get him and bring him home. And then proceed with blood work. I feel better now. Will keep you all updated.

Just spoke with the vet. It was like pulling teeth, but I finally got her to say that she thinks it's unlikely that Charlie has rabies. THANK GOD! And why did they have to bring me so close to making a decision to ethanize him? So here's the lesson, folks. When your animal becomes suddenly ill and you're forced with a decision to euthanize, WAIT!

Thanks for all the kind replies, everyone. It looks like the rabies scare is behind us. I told the vet this morning, "if he has rabies, it's going to progress rapidly, right?" She didn't want to confirm that, but finally did. Then I said, "so, if he's better today, and better tomorrow, then he can't have rabies, right?" And finally, she said "Correct." I think this was all unnecessary. And I'm starting to think maybe his reaction was caused by the antibiotics. We'll see. I pick him up at 8 AM. Can't wait.