The Theory of Sleep Communication describes the method and its requirements by which it is possible to send messages with arbitrary content from the wake world to the sleep world and vice versa from the sleep world to the wake world, using dream incorporations, lucid dreaming, body signaling and a message coding scheme.
Sleep communication as described in this theory has to be distinguished from two related, but different phenomena. First, the term sleep communication describes the conscious, deliberate answering to messages by a sleeping person, and thus is different from subconscious reactions to stimuli during sleep. Second, sleep communication has to be distinguished from talking under hypnosis. As Spiegel and Spiegel (2004) write, these are two different mental states: “The hypnotized person is not asleep, but awake and alert.” The Theory of Sleep Communication focuses on communication with sleeping people, not hypnotized people.