Fibromyalgia can cause generalized weakness, affecting all your muscles at once, or weakness in a particular muscle. Your muscles may be easily exhausted and respond by trembling or twitching. In fibromyalgia, your muscles may be tight or tense much of the time, leading to soreness and pain.

I seem to recall reading that this jerking could be a side effect of one of the drugs commonly used to treat fibromyalgia. Lyrica? If you are on meds, you could check with your pharmacist.

I have major cramps that wake me up. It feels like those charlie horses that you get in your calves. Only I get them throughout my body. It has gotten to the point, that I have to take a pain pill before bed just to get some sleep.

Yes I had that. It seemed to be caused by Lexapro. One time the jerk nearly threw me out of the bed. It stopped happening when I stopped the Lexapro..

Sure do plus muscle cramps, ouch!