Nonrestorative sleep.

The current review presents the empirical findings on varying definitions of nonrestorative sleep (NRS). Despite lacking a standard, operational definition, NRS is investigated in research studies and included in diagnostic manuals. However, because of the absence of standardization, the conclusions that can be drawn about NRS based on the current body of empirical literature are limited. A feeling of being unrefreshed upon awakening that is not accounted for by lack of sleep may occur among a substantial percentage of the population. This experience is correlated with daytime impairment, pain, fatigue, and electroencephalogram (EEG) arousals in non-REM sleep but causal links are unsubstantiated. An immediate converging of researchers toward NRS standardization is needed. We conclude that conceptualizing NRS as a primary symptom of insomnia on par with difficulty initiating sleep and difficulty maintaining sleep is empirically unsubstantiated. We recommend defining NRS as a report of persistently feeling unrefreshed upon awakening in the presence of a normal sleep duration, occurring in the absence of a sleep disorder.