What is sleep? Why do we sleep? How much do we normally need, and what happens if you don't get enough sleep? Are we modern people with busy lives suffering stress from 'sleep debt'? This book is about all aspects of sleep. It's a subject that interests and worries a lot of people. In recent years, the nature of sleep, our sleeping patterns, how much sleep we need, and the dangers of lack of sleep have become increasingly important, as people work longer hours, styles of working have altered, and the separation between workplace and home has been eroded by the mobile phone and the Internet. From drowsiness at the wheel, to stress and insomnia, this is a subject that matters to people.