Sleep-talking usually occurs during transitory arousals from REM sleep. It can also occur during NREM sleep at which time it represents a motor breakthrough (see sleep paralysis) of dream speech (the words spoken in a dream are uttered out loud). Full consciousness is not achieved and the sleep talker is not aware of his/her vocal output.
Sleep-talking can occur by itself or as a feature of another sleep disorder such as:
REM sleep behavior disorder (RBD) - loud, emotional or profane sleep talking
Night terrors - intense fear, screaming, shouting
Sleep-related eating disorder (SRED)
Sleep-talking is very common and is reported in 50% of young children, with most of them outgrowing it by puberty, although it may persist into adulthood (about 5% of adults are reported to talk in their sleep). It appears to run in families.