Meanwhile, your heart pounds in dread for all the horrors that undoubtedly await you on the morrow—should you live till then. You feel a jab of panic. Sleep, dammit! You're going to feel like crap all day tomorrow,you may order yourself, feeling your heart pick up speed at the thought.
If you're lying next to someone, you listen resentfully to that person's deep, regular, innocent, animal breaths, hating him or her for not joining you in your night of sorrows. If you're by yourself, you might sigh, sit up, turn on the light, arrange the pillows behind you, and begin reading the book that you almost fell asleep over just a few short hours ago. But you can't concentrate very well—you feel exhausted and wired at the same time, preternaturally alert and jumpy, but with a deep, penetrating tiredness. After reading the same paragraph 12 times, you get out of bed, go into the bathroom, turn on a light, pee, and take a look in the mirror at your haggard face.
It's now 3:42, and you begin wandering aimlessly around your house like the undead, looking out different windows at the quiet nighttime neighborhood. You know with great, hallucinatory certainty that everybody in your community, your town, your state, everybody within four to six time zones, uncounted millions of people are all peacefully asleep—all except you. You, however, are wide, wildly awake, and absolutely, utterly alone.
Insomnia. Almost everybody has it at one time or another. Some poor souls live (or barely live) with it. It's hard to know exactly how widespread it is—prevalence rates are all over the map. As many as 30 percent of the population, or as few as 9 percent (depending on the source of the statistic, or how insomnia is defined, or what impact it has), suffer from some form of it at least some of the time. Critics maintain the higher estimates are overblown, partly by insomniacs themselves, whose suffering leads them to overestimate the time they spend lying awake (10 minutes of lying wide-eyed in bed feels like an hour) and by the pharmaceutical industry (that all-purpose villain) in order to sell billions of dollars in sleeping potions.
Definitions of insomnia are loose to the point of inanity. DSM-IV defines "primary insomnia" as "a difficulty initiating or maintaining sleep or experiencing nonrestorative sleep that results in clinically significant distress or impairment in functioning." Insomnia has been divided and subdivided into a bushy tree of overlapping categories: primary, comorbid (occurring with a boatload of mental and physical health problems), idiopathic (lifelong inability to sleep), psychophysiological (somaticized tension), paradoxical ("sleep-state misperception") childhood ("limit-setting sleep disorder"—parents don't enforce bedtime), food-allergy related, environmental, periodic (internal clock problem), altitude related, hypnotic, stimulant-dependent, alcohol-dependent, toxin-induced, menopausal, and age-related, among others.