Hi and welcome,
In neurological conditions like MS, Lhermitte's (shock like sensation) is an indicator of lesions in the cervical spine and the trigger is movement of the neck, the damaged nerves in the spinal column are basically stretched and it causes the electric shock like sensation.
Lhermitte's sign is common in MS, but it's not exclusive to this disease, people with spinal cord injuries, cord inflammation, cervical spondylitis, disc impingement or degeneration, vitamin B-12 deficiency, hormonal conditions like menopause, mental health conditions etc etc also experience the electric shock sensation too..
To give you an example of how mental health issues like anxiety which is a fairly common causes of electric shock sensation occurs...
"Behaving apprehensively (anxiety) stresses the body. Stress affects the body's nervous system, which is primarily made up of neurons - cells that have an electrochemical property (chemistry and electricity). When the body becomes overly stressed, the nervous system, which includes the brain, can act involuntarily and erratically. This in voluntary and erratic behavior can cause sudden 'shock-like' feelings in any one part, or throughout the body. The electric shock feeling anxiety symptom is a consequence of stress and how it adversely affects the body.
While the electric shock anxiety symptoms can be startling, and even unnerving, they aren't an indication of something more serious, nor are they harmful. You don't have to worry about them. Simply reducing your anxiety and your body's stress, and giving the body ample time to calm down will eliminate the electric shock feeling anxiety symptoms. Therefore, they needn't be a cause for concern." http://www.anxietycentre.com/anxiety-symptoms/electric-shock-feeling.shtml
....i would suggest you discuss this experience with your family dr, basic blood tests may be all that's required to find the underlying cause.
Hope that helps....JJ