If you look on the Fibromyalgia board or do a search they talk about this alot. I'm not sure if it's directly linked to MS or Fibro, but I hear it more often on that board. You should check it out.
I myself have been on that board less and less because even though I'm awaiting an MS dx, I already have a Fibro dx, but I don't have alot of the symptoms. Mostly just the fatigue and some pain.