F2U,
I get that when I have a relapse. My MS Neuro I had in the way early days said it was "Myoclonic Jerks". I rarely get them anymore, but you feel that quick shot of pain and then the leg shoots upward, I noticed this only in the recliner or in bed. Maybe once or twice and that's it per day with relapse.

Is that what you mean? This may help to read.

http://en.wikipedia.org/wiki/Myoclonus