shakes and spasms

I have bouts here and there where my entire body, including legs twitching, head bobbing, hands twitching etc.

I have Rheumatoid Arthritis and Fibromyalgia.

Do Not Have:
thyroid problems
MS
allergies


When this happens, my entire body goes into a freak attack where it feels like the shivers all over and slight burning in the muscles.  After a while it stops and my muscles feel like they are relaxing.

When this all starts, i have to sit down fast or I will fall from the weakness of my muscles.

I wish i knew what this was.