Sleep and dreams have always been shrouded in mystery, inaccessible to human understanding. Why do we lose contact with the outside world every day? Why do you need to sleep? Should we attach importance to dreams and why do people even see them? Explanations were sought for the mysteries of sleep, both mystical and scientific. The emergence of new methods for studying brain activity, modern capabilities of genetic and biochemical research have made it possible to find out why, how and how much we sleep in reality. What today's science knows about sleep - as well as about such conditions as insomnia, lethargic sleep, lucid dreams and much more - is described in this book.