I have had ms for nearly 9 yrs now, and L'Hermittes was my main presenting symptom. I had it on and off for many years (along with other stuff), and yes, it often goes away. Unfortunately, I have had it permanently for the past year (since a couple bad relapses in 2006), along with many other worsening issues (not relevent here).
It can present as tingling/pins and needles or electric shocks down your back to your legs/feet or arms/hands, on either side or both, when flexing the neck - bending your head forward. Sometimes slight movement can provoke it, and sometimes it takes serious flexion - really depends on where in the c-spine the lesion is and how far it extends.
In ms it is caused by a lesion or inflammation in the c-spine (but it can be caused by other things, like cervical spondylosis, disc degeneration etc).
If you do have a c-spine lesion, you may find that the tingling disappears as the inflammation subsides - this is usually what happens, and if you don't get other lesions in those areas, you may never have the tingling again!
Best of luck, keep running, and I hope you do well.