I used to have this and M.S. when I had mercury filling poisoning (also, you may want an MRI to rule out cervical spinal stenosis):

Lhermitte's Sign:

(electrical sensation passing down the back when you flex your head forward) and paroxysmal (brief) pain in the arms and legs. These symptoms are usually triggered by touch, movement or even hyperventilation (rapid breathing).

When treating acute pain syndromes with drugs, doctors turn first to anticonvulsant medication. Carbamazepine (Tegretol) is the first drug of choice. Other drug therapies include Gabapentin and Dilantin. These medications block abnormal conduction at the demyelinated site in the central nervous system. 

Generally these acute pain syndromes are time-limited, but may last days to weeks. Many people will tolerate annoying medication side effects to manage their pain during this period.

Lhermitte's sign: Flexion of the neck in patients with multiple sclerosis produces electric shock-like sensations that extend down the spine and may shoot into the limbs.

http://en.wikipedia.org/wiki/Lhermitte%27s_sign

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.

Typically, the electric shock-like sensation radiates from the neck downwards and lasts for a very short duration; usually less than a second. The sensations can repeat indefinitely so that it might feel almost continuous.

The areas affected by Lhermitte's sign are usually the arms and / or the legs, although the sensations can radiate to the trunk.

Lhermitte's sign gets its name from the person who first characterized it, Jacques Jean Lhermitte, and is sometimes (rarely) known as 'barbers chair phenomenon'.

This is because of the way that Lhermitte's response is triggered; by flexing the neck forwards. When the head moves in this way, the electric shock like sensations are triggered.

Torrie