Imagine waking up to find you can't move a muscle. It's dark, but you're sure you feel a presence in the room, hovering near your bed — or perhaps sitting on your chest, crushing the breath out of you.

Many of us try to sleep as little as possible. There are so many things that seem more interesting or important than getting a few more hours of sleep, but just as exercise and nutrition are essential for optimal health and happiness, so is sleep.