Random loss of use of back legs

Question
About two weeks ago we noticed our house bunny had fleas, so we combed him and applied a flea spray made for rabbits and hamsters.  He's about 11 years old.  I combed him every two or three days, but the fleas were not completely gone after several days so we reapplied the flea spray.  When we put him down after applying the second round of flea spray we noticed he was hopping crooked and then fell down--he had lost the use of this back legs.  He was eating and drinking well, but couldn't hop.  His condition slowly improved over about two days, and he was back to normal but now has episodes where he will completely lose his ability to move his back legs.  It usually lasts less than a minute and then he's fine.  Do you have any idea what is going on?  Could it have been caused by the flea spray?  We haven't used it on him since the first incident.  Could this be caused by the fleas themselves?  Or do you think he may be having seizures (I thought I saw him have one once a long time ago, but never since).

Answer
If he has had a seizure in the past, it might be that. Different things can trigger them, including the stress of fleas and being treated for them. Does he just loose the use of his back legs, and nothing else happens? Usually seizures actually have the rabbit freezing up and/or sort of shaking on the floor on their side.

It is possible it was caused by the flea spray, if he has any conditions that would have made it so he was sensetive to the spray despite it being okay for small animals. This would be a fairly rare case, though.

Fleas also can carry diseases and parasites, to it is possible they passed something onto him. The parasitic protozoa E. cuniculi is known for leg paralysis, so that may be the cause. Getting him in to the vet to be tested for it would be the best thing, if that is at all possible. E. cuniculi can cause a lot of problems, including death, if it spreads to other areas of the body. Stresses from the fleas might also have triggered a population boom of the protozooa if it was already in the body. Some rabbits have it, and it never affects them until they are stressed by something unusual (such as other parasites or infections).