Fibromyalgia and fatigue: central processing, widespread dysfunction. 
Biological and psychological bases for the covariation of pain and fatigue in fibromyalgia (FM) are reviewed.  FM is characterized as a disorder of central sensitization, with pain and fatigue as the most prominent symptoms.  The roles of sleep disturbance and affective dysregulation as both precipitants and consequences of pain and fatigue in FM are discussed.  It is argued that a positive affective disturbance may uniquely characterize pain and fatigue symptoms in FM.  Finally, pharmacological and nonpharmacological treatments for FM are highlighted, with an emphasis on the efficacy of these treatments in alleviating pain and fatigue symptoms.