Sleep problems are very common in people that have fibromyalgia syndrome(FMS). I saw an abstract for a study published in the journal Arthritis and Rheumatism that was done to determine the prevalence of sleep problems in FMS. Over 12,000 women without FMS were followed for upto 13 years and asked about sleep problems and FMS symptoms. Of note, no physicians diagnosed these women with either FMS or a sleep disorder - all the information was self-reported by the women themselves. The results showed that there was a dose-dependent relationship between sleep problems and FMS - meaning that the more frequent a woman reported sleep difficulties, the more likely she would also have FMS. The association was especially strong in women greater than 45 years old.
The results do not help us understand if FMS leads to sleep problems or the reverse. Since diagnoses were not made by physicians, it's difficult to know if the women with sleep problems had insomnia secondary to the FMS or another sleep disorder like obstructive sleep apnea, which can cause insomnia and is more common as we age. I have had patients with FMS feel like they can tolerate their pain better when they sleep better - this implies that sleep difficulties at least contribute to pain tolerance.