What I would do for now:
Put him in a small cage, or carrier so he doesn't even try to move. Enough hay or so as bedding so he stays reasonable dry when he pees. Put his food and water right in front of his nose, so that he doesn't have to move. Whatever is going on, it is important that he keeps eating. Give him rest.
If it is a severe spine injury, like from a fall, that wouldn't go away. But sometimes, as I've read, if nothing got severed a swelling or bruise can cause temporary paralysis, but without a vet and x-rays I wouldn't know a way to tell if it's a permanent damage or not.
There is a facebook group of people with disabled rabbits (I don't do facebook so I don't have a link),, maybe you get tips there.