One more thought: Canine narcolepsy gets much worse when the dogs are excited (ie, during feeding). It is due to a defect in a certain receptor in the dogs' neurons. When I mentioned the spider ball "wobble" to my neuro prof last year, he said it sounded like it could be something like that (a receptor mutation or neurotransmitter deficiency).

Also, the spider "wobble" seems fairly similar to the Enigma loopies (from what I know about it -- not into leopard geckos at all). I recall reading mention of a study that did MRIs on Enigmas and found no visible anatomic defects, suggesting a problem on a molecular and not anatomic level.

Neuro + genetics + snakes = I geek out.