Human consciousness and sleep/waking rhythms: a review and some neuropsychological considerations.
Journal of clinical neuropsychology September 1, 1982 R Broughton
Consciousness is often thought to be absent during sleep, but evidence from literature and personal studies shows that rich subjective experience continues throughout sleep, much of which is not recalled later. This suggests William James' 'stream of consciousness' persists continuously across sleep and wakefulness, with memory recall problems interfering with reporting. Sleeping subjects show selective awareness of external stimuli; significant stimuli typically cause awakening, while nonsignificant ones may be incorporated into ongoing REM or NREM mental activity. Sleep mentation is highly autonomous with little willful control. Creative insight and problem solving can occur in sleep.