What makes people talk in their sleep?

Sleep talking often occurs in the absence of a pre-existing condition and is usually harmless, according to WebMD. However, sleep disorders, such as sleep terrors and REM sleep behavior disorders, may cause shouting during sleep.

Nocturnal sleep-related eating disorder and sleepwalking may also cause sleep talking, states WebMD. Furthermore, emotional stress, fever, certain medications, substance abuse and mental health disorders may be other causes for sleep talking. Also known as "somnliloquy," sleep talking may range from gibberish and mumbling to coherent and complex narratives. The content of sleep talking is often random, but sometimes it may be related to present or past experiences.