Why does the kind of stiffness that can be likened to rigor mortis occur in the body of someone with fibromyalgia; are there any clues why that could happen in a living-breathing person? Rigor "stiffness" mortis "of death" says it all really....it is a condition of death so what makes it appear within life for just so many people, resulting in a kind of half-life. I had been here before but this time I wanted to get to the bottom of the mystery...