I had that internal trembling during one period of my life, perhaps 30 years ago. It lasted a couple of months and I took Choline to control it. I don't have that now.
But I am a champion twitcher. I call it Myoclonus. Back and legs jerk, mostly at night after I have relaxed in bed. I control it, as I've often said here, with magnesium and calcium. I have close to complete control with that, if one compared it to how it would be without magnesium...I went one night without it in the hospital and never stopped the myoclonus once. They should have got me magnesium as I asked. They were too busy.
I hope you've tried mag, Skywalker. MS doctor prescribed it for me long time ago.