This film explores the strange and relatively unknown world of sleep-a world in which we spend approximately one third of our lives. The Mystery of Sleep shows how the discovery of REM (Rapid Eye Movement) during our dream period in the early 1950's by Dr. Nathaniel Kleitman at the University of Chicago, brought about a much broader understanding of the mechanism of sleep. Before his discovery it was believed that during sleep the brain was in a state of rest. Dr. Kleitman's discovery opened up explorations of the nature and frequency of dreams and nightmares, and sleep disorders such as insomnia, apnea and narcolepsy that affect millions of Americans.The film uses computer-generated images to illustrate dream cycles as well as the state of "active paralysis" in which we usually sleep. Featured are some of the leading figures in sleep research such as Dr. William Dement of Stanford University, who has authored and co-authored more than 500 scientific publications on the subject, including the book The Promise of Sleep. Despite all the advances in this field, a researcher comments, "We know more about Mars and Venus than about sleep".