Stage One - Person relaxes into sleep and is characterized by passive, restful state of mind. Stage Two- The person drifts into deeper sleep and may feel a pleasant sense of falling. Hypnogogic and stationary images drifts before the mind's eye. Stage Three - This is an intermediate level of sleep and in the stage, large body movements may occur. Stage Four - This stage is characterized by very little body movement and the body is deeply relaxed. Sleepwalking and nightmares (unpleasant emotional arousal) may occur but they are not accompanied by dreams (vivid visual images)

The non-dream sleep repeats itself every 90 minutes and the body makes a transition from the deep stages (3/4) to the earlier stages (1/2). During this transition, a new sleep pattern known as dream sleep may occur. In dream sleep, the eyes tend to move quickly under the closed eyelids (Rapid eye movement, RAM Sleep) and large skeletal muscles become flaccid.

The meaning of dreams have been interpreted in many cultures. Sigmund Freud suggested that the content of a dream conceal a hidden content which expresses some form of wish (often dealing with sex and violence) that is not acceptable to the conscious mind. Psychoanalytic theorist such as Carl Jung believe that dreams are the language whereby the unconscious mind communicate to the conscious mind. Many psychologist believe that dream is a way brain cleans out various unwanted memory. Other brain scientists however suggest that dreams have no meaning.