I am not sure about spondylosis, but having seen some x-rays of it, the idea that there are spurs all along the spine that can cause pain and possibly tissue damage is what I based that idea on. I could imagine a spur high up on the spine putting pressure on the brainstem to cause some uncontrollable movements.
If I remember, vertical and positional nystagmus are more common for neurological-issue infected bunnies, and horizontal is for ear infections. This describes the way the eyes move.
Positional nystagmus describes that the eyes don't move in coordination with the body moving. For instance, if you're looking at something and you turn your head, your eyes move in their sockets so that you can continue to focus on what you were looking at. We don't have to think to do this, it just happens. The brain takes info from the vestibular system in the ears (that tells you which way is up, and if you're moving--the inner ear stuff) and processes it, and sends info to the eyes to make them move in a way that corrects for this. A lot of this is done by some lower/back of the head brain structures, near the spine. If your body wasn't able to do this, it would be positional nystagmus. I'm not sure how you'd test this in Jack, though. You'd have to get him to focus on something and then move his body and watch if his eyes move too.
http://www.rabbit.org/health/tilt.html
(I've taken a ton of neuroscience courses, so please let me know if that description was too technical.)
I know that you can handle this, and when you and Jack can't take it anymore, you'll know. He is getting great care and is having some happy days. He gets all the food he wants, baths, naps in the sun, and time with the people and rabbits he loves. [[hugs]]
