A growing body of literature suggests that sleep plays a critical role in emotional processing. This review aims at synthesizing current evidence on the role of sleep and sleep loss in the modulation of emotional reactivity, emotional memory formation, empathic behavior, fear conditioning, threat generalization and extinction memory. Behavioral and neurophysiological evidence suggesting that rapid-eye movement (REM) sleep plays an important role in emotional processing is also discussed. Furthermore, we examine the relations between sleep and emotions by reviewing the functional neuroimaging studies that elucidated the brain mechanisms underlying these relations. It is shown that sleep supports the formation of emotional episodic memories throughout all the stages that compose memory processing. On the contrary, sleep loss deteriorates both the encoding of emotional information and the emotional memory consolidation processes.

Research is also progressively providing new insights into the protective role of sleep in human emotional homeostasis and regulation, promoting adaptive next-day emotional reactivity. In this respect, evidence converges in indicating that lack of sleep significantly influences emotional reactivity. Moreover, notwithstanding some contradictory findings, the processing of emotionally salient information could mainly benefit from REM sleep. However, some crucial aspects of sleep-dependent emotional modulation remain unclear.