From Goldenberg (Arch Intern Med, 1999)  

CONCLUSIONS 

Fibromyalgia is a clinical syndrome... Medicines that affect pain perception, sleep, and mood have been useful and should be integrated with activity, exercise, and educational programs. Most patients with FM observed in tertiary referral centers report little change in their symptoms over time. The outcome is directly related to psychosocial factors, including past and current psychological distress and work status or disability issues. As with any chronic illness, patients in the community do better than those observed in specialty clinics. Ten percent to 30% of patients describe being work impaired from FM. Physicians should discourage inactivity and disability because, if these are prolonged, there is an adverse effect on prognosis. Finally, patients have found a diagnostic label to be reassuring, and the diagnosis has decreased costly testing and health care use. ...

Emphasis added.