Why are we distracted, tired or lazy at different times during the day? Why do we fall ill? Medicine has always sought the replies to these questions in our waking state. On the contrary, sleep research looks for them in an, as of yet, poorly understood state: sleep. "The Mistery of Sleep" introduces the audience to the mysteries of sleep through a series of personal stories and emblematic cases of irregular sleep, excessive sleep or total lack of sleep. Why does a man keep falling asleep at work? Why does a former boxer sleep twenty hours a day? How can a painter sell his paintings before painting them? Can we live without dreaming? These different accounts will be commented on by the world's leading authorities in sleep research.