TIME reveals the cutting-edge science of sleep: why you need it, what happens when you do it-and what happens to your body and brain when you don't. Learn how to squash nightmares and dream yourself to better mental health; uncover how to improve your metabolism and weight through rest; discover which sleep apps can actually help you; and find out why you should be wary of sleeping pills. Finally, you'll also get the nine new sleep rules-a recipe for the best night's sleep of your life.