It's a pain in the butt, that's what. There is always non-restorative sleep. FMS patients do not get much, if any, stage 4 Delta sleep. Muscles do not recover overnight as in normal individuals, hence the pain and stiffness.
Depression can set in as with any chronic condition.
There are many other accompanying symptoms that can occur as well. There must be pain on both sides of the body, pain above and below the waist, and on the spine. This must produce a report of pain on 11 of the 18 tender points in order to make the diagnosis of Fibromyalgia Syndrome. A syndrome, not a disease, Fibromyalgia does not cause degeneration of body organs or tissues, nor does it deform. One patient may hardly notice the effects of FMS while another may be severely disabled.