It sounds like e cuniculi, a parasite that affect the nervous system.
Your rabbit will need a specific blood test to verify the presence of e cuniculi, and then treated with specific de-worming medication.
Left untreated, e cuniculi can spread to the liver and kidneys, cause incontinence, and paralysis. I recommend you revisit the vet with all the relivent literature you can find, or travel to a rabbit-savvy vet. These are just a small sample of information available that you can print out:
http://www.medirabbit.com/EN/Neurology/cuniculi/pyrimethamine.htm
http://www.hrschicago.org/cuniculifr.html