Night naturally calls forth our shadowy inner life. Because we lose the visual input we depend on to define ourselves and our behaviors, we get lost in the dark. In more primitive settings and times, our ancestors faced the risk of unseen dangers lurking in the night. Many are familiar with Job's bleak description of his plight: "I go to the place of no return, to the land of gloom and deep shadow, to the land of deepest night, of deep shadow and disorder, where even the light is like darkness."
Who hasn't had at least a brush with the dread of darkness—perhaps swallowed by the pitch-black of a power outage, overwhelmed by the immensity of a frozen night sky, or, most commonly, lying alone and awake in the darkest hour of night? We're afraid of that nothingness—of being consumed by that unknowable void. And that's precisely where sleep takes us.
Traditionally, sleep and darkness have had more positive connotations. Nyx, the mighty Greek goddess of night, lived underground and ascended to the sky at day's close to bring dusk and darkness. Her son, Hypnos, the sweet-natured god of sleep, would accompany her each night, sprinkling sleep-inducing poppies over the earth below—a story prefiguring the more recent folktale of the sandman sprinkling sleep dust into the eyes of children. This ancient myth reminds us of two fundamental truths about sleep: it's born of night, and it's a divine endowment—a gift from the gods. To enter this blessed state, the myth suggests,…