Sleep and pain: interaction of two vital functions.

Disturbed sleep is a key complaint of people experiencing acute and chronic pain. These two vital functions, sleep and pain, interact in complex ways that ultimately impact the biological and behavioral capacity of the individual. Polysomnographic studies of patients experiencing acute pain during postoperative recovery show shortened and fragmented sleep with reduced amounts of slow wave and rapid eye movement (REM) sleep, and the recovery is accompanied by normalization of sleep. Objective assessments of sleep in patients with various chronic pain conditions have been less definitive with some studies showing fragmented and shortened sleep and others showing normal sleep. Although daytime fatigue is a frequent complaint associated with complaints of pain-related disturbed sleep, objective assessments of daytime sleepiness reveal minimally elevated levels of sleepiness and emphasize the importance of distinguishing sleepiness and fatigue. The pain-sleep nexus has been modeled in healthy pain-free subjects and the studies have demonstrated the bidirectionality of the sleep-pain relation. Given this bidirectionality, treatment must focus on alleviation of both the pain and sleep disturbance. Few of the treatment studies have done such, and as a result no clear consensus on treatment approaches, much less on differential etiology-based treatment strategies, has emerged.