Episodic thought distinguishes spontaneous cognition in waking from REM and NREM sleep

• Episodic thoughts of the past and future rarely occur in either N2 sleep or REM sleep. • In contrast, episodic thought is a common feature of waking spontaneous thought. • Episodic thoughts in wakefulness tend to be future-focused and involve planning. • Autonoetic consciousness may differentiate spontaneous thoughts in sleep and wake. Evidence suggests continuity between cognition in waking and sleeping states. However, one type of cognition that may differ is episodic thoughts of the past and future. The current study investigated this across waking, NREM sleep and REM sleep. We analyzed thought reports obtained from a large sample of individuals (N = 138) who underwent experience-sampling during wakefulness as well as serial awakenings in sleep. Our data suggest that while episodic thoughts are common during waking spontaneous thought, episodic thoughts of both the past and the future rarely occur in either N2 or REM sleep. Moreover, replicating previous findings, episodic thoughts during wakefulness exhibit a strong prospective bias and frequently involve autobiographical planning. Together, these results suggest that the occurrence of spontaneous episodic thoughts differs substantially across waking and dreaming sleep states. We suggest that this points to a difference in the way that human consciousness is typically experienced across the sleep-wake cycle.