This sounds like wry neck and it CAN be mostly cured in an unorthodox sort of way.
Back when we were raising Flemish Giants we had a couple that developed this. Everything we read said they were going to die and after having raised rats with similar problems, we came to terms with the fact that the first Flemish who developed it was going to get worse and die.
Being, well, a giant, we decided to let him loose in our backyard so he could at least spend his last few days munching on grass. Then we figured we'd dispatch him once he became too sick to move.
Within a few days he was almost back to normal. Within a couple of weeks his head had straightened out and he was fine. If you picked him up he'd "roll" and one of his ears usually half-lopped on the side his head used to tilt, but otherwise he was fine.
We never put him back in a cage. He'd sleep in the barn at night and roam our yard during the day. When we were out in the yard he'd run circles around our feet and act like a big dog. We had him out there for at least two years, maybe three, before he passed away.
Our second case of wry neck was also in a Flemish Giant and we immediately plunked him on the ground, too. He was in the yard for around a year before the neighbor's new dog managed to get him. His head still tilted a little to the side, but he was able to live a normal life.
We didn't medicate either of the rabbits. This was around ten years ago when the treatment for wry neck was to put them out of their misery. I came to the conclusion that cramped conditions was either one of the causes of wry neck, or wide open spaces was a sort of cure. If you can pull off something like this (even a large "rabbit tractor" that is nice and tall) then you may be able to at least make him comfortable. If you can litter box train him then he can become an indoor pet, either for you or someone else. I don't recommend breeding him in case wry neck is genetic (even partially genetic).
Good luck with him.
