I am worried that your rabbit may have sustained a back injury. As you know, rabbits have very strong muscles in the back legs and a fairly light bone structure. This makes it easy for them to dislocate, or fracture the spine.
Usually when this happens, there is not much pain because the spinal cord has been damaged causing paralysis and loss of sensation to the back legs. If the spinal cord has not been permanently damaged, medication and restricted activity can sometimes lead to enough healing that some function is regained. I recommend taking your bunny into the vet as soon as possible to have it evaluated and treatment started. time is of the essence!
Permanent paralysis will lead to problems urinating and defecating, digestive problems and pressure sores, and significant nursing care to provide a quality life.
I will cross my fingers that there is no permanent damage.