Lots of people talk in their sleep. Doctors call it somniloquy. Sleep talkers can whisper mumble or shout. Sleep comes in cycles. There are five parts to a sleep cycle. The first is when you begin to fall asleep. This is called light sleep. In the next part you are asleep. You do not notice things around you. Then come two stages of deep sleep. Your muscles are relaxed. Your body repairs itself. It fixes bones and muscles and fights off disease. Last is REM sleep. This is when you dream. The whole cycle lasts about one and a half or two hours. When it ends a new cycle starts. Sleep talking can take place any time in the sleep cycle. People talk in their sleep when they are stressed.