"True" L'Hermittes indeed originates with the nerves in the neck, and radiates down from there. Sometimes down through a shoulder, other times down the spine to the butt, and even in to the leg. It is initiated by bending your neck.
Here is a web page that describes it: http://www.mult-sclerosis.org/LHermittessign.html
Other zaps and zings in limbs (and elsewhere) might be an indication of peripheral nerve problems, or sometimes just "happen" (folks without neurological problems can and do get zaps and zings from time to time, when a nerve is touched. )
...I am not a doctor, nor health professional, and don't pretend to be one, here.....