I'm not really sure what it is. I hope the doctors can figure it out. Did it start when you had your car accident? I'm thinking maybe something in your vertebrae was damaged in the accident and slips around, pinching a nerve. Or maybe it's muscular damage that is affecting nerves and/or blood circulation. If it is muscular inflammation, it could explain why Ibuprofen would help. I wonder if some gentle stretching when you're not having these episodes would help.

Please update after you see the neuro.