Re: what causes electric shock sensation
L'Hermittes is one of many indicators for MS. In my case what happened was this: I would look down at my feet (bend my head foreward while sitting upright) and I would get shock like feelings in my feet. It is, I believe, caused by lesions at or near the top of the spine. The electrical impulses the act of bending your neck creates, or perhaps the signals needed to bend your neck, are 'short circuted' causing the shock like symptoms to be sensed elsewhere, in my case the feet.
Keep in mind that I am not a neurologist so this may not be correct but it is my understanding of it. The good thing about this board is that there are many members here who have much more experience and knowledge and will give you the benefit of their understanding.