What you're explaining sounds a lot like L'Hermittes sign.

L'Hermittes sign is the name given to an electric shock-like sensation which often presents itself with multiple sclerosis; although Lhermitte's sign is not exclusive to ms and may be the result of some other conditions such as electrolyte imbalance, cervical cord tumour, cervical spondylosis, or even vitamin B12 deficiency. http://www.themcfox.com/multiple-scl...ittes-sign.htm