What you are describing appears to be consistent with a neurologic problem. A veterinary neurologist evaluation would be helpful. If you can video tape an 'episode' for the neurologist to see, that would also help them. The things that I would think of would be congenital/developmental, infectious (bacterial, viral, fungal), infammatory, toxic or metabolic. It may be just affecting the motor coordination or it may even be an underlying local seizure disorder.
I hope this helps. Wish I could give you more specific information.