The next time you catch yourself lamenting the lack of mystery in modern life, consider how little scientists know about sleep. Why we sleep, not to mention how, remains unknown. Theories abound, of course, especially among those who hope to concoct a better sleeping pill, but the riddle of sleep won't be solved by a new drug. The deeper wonder is how easily most of us slip under without taking a thing. Sleep is a reminder that humans, like all earthly life, are shaped at the deepest level by the whirling of celestial spheres. Sleep also dissolves our sense of self, reducing us each night to what we were before waking to the world. Maybe that explains the unique anguish of insomnia, which cruelly denies its sufferers a brief escape from their own company. Or maybe not. As the following articles suggest, in every age and culture, the mystery of sleep outlives all explanations. -The Editors

I would steal an hour of my lover's sleep if I could. I would slip beneath his eyelids and yank it right out of him. He would feel nothing. Nor would I-neither remorse nor shame. One hour of perfect unconsciousness: one clean, soundless dive, deeper and deeper, as far as my lungs would take me. I would come up for air before he woke. Instead, I lie motionless, sewn to the sheets by the smallest demons, watching Steve's silhouette against the bedroom blinds. Fondness becomes hostility. How does he do this for eight hours? I listen to his tranquil breathing, furious that he sleeps while I cannot.

Finally, at 3 a.m., I snip the threads, discard my carcass at bedside, and leave it behind in disgust. Time for the insomniac to make his rounds. I creep into the next room, where I feel a thrilling freedom from my own body. I am naked, but not cold; not thirsty or hungry; I can smell nothing. My eyesight is shot; I cannot face the TV, work, or read. The plug has been kicked out of the socket, the circadian clock stopped, and I roam the apartment of my own power, on my own theory of time, occupying a fragile space between dreaming and functioning.

A doctor would tell me that sleeplessness in this form may harm, but can never kill. The distinction is far more subtle, as only lifelong insomniacs know: Chronic sleep deprivation transports the body, as through a time warp, into a condition in which it cannot be killed. As much as you might wish for it, the body will neither sleep nor die. By the time I cross this line, the stress and anxiety that first kept me awake are gone. I am beyond the phase of tossing and turning as I worry about a nagging problem--something everyone experiences occasionally. One hour of sleep lost the first night turns into two the next and four the night after. Sleeplessness feeds on itself, reproduces, and quickly becomes the source of apprehension. This severe insomnia visits me at least once a year. I may live with it for weeks--often dozing just two hours per night--before ordinary rest returns.