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Let's follow you through a typical night's sleep.
When you lie down to sleep in the evening, you've already established, by your routine, several necessary conditions for you to be able to go to sleep. You've checked the security of your house, protecting yourself from danger. You've opened the bedroom window for fresh air and adjusted the covers so you are just the right temperature. You've bunched up the pillow so your head is neither too high nor too low. You've read for a while (nothing too spicy) so your mind can ease away from the stimulations of the day, and, of course, you've turned out the light, decreasing the sensory input to your resting brain.
These conditions are very important for the process of initiating sleep. Many people find it impossible to go to sleep until certain requirements, which vary from person to person, are met. Once these conditions are met, you lie quietly in bed anticipating sleep.
What Is Sleep? It's fairly difficult to define sleep precisely, but an acceptable definition is that sleep occurs when one is no longer aware of the external environment. Lying in bed, you are still well aware of the ticking of the clock or the breeze rustling the leaves outside the window, or, perhaps, even the quiet of the room - you're simply resting; you're not yet asleep.
The time it takes to go from this resting state to sleep varies tremendously, but it's often short - about fifteen minutes. Most believe that falling asleep is gradual, but entering sleep is sudden, often just a few seconds. In an interesting experiment, several subjects had their eyelids taped open and a bright strobe light flashed before them every second. The subjects were instructed to press a small button after each flash to confirm that they had seen it. For ten or fifteen minutes they regularly tapped their responses to the flashing light. Suddenly, they stopped - they had fallen asleep in an instant. When awakened at that time (yes, it is possible to fall asleep with your eyes taped open), they reported that they did not remember having missed any flashing lights at all! What happened? Within a second or two, they went from being awake to being asleep.
The Twilight Zone When you are truly asleep, you are not responsive to the outside world. Sleep researchers have identified five different patterns, or stages, of sleep and you have just entered the first one, which I call "the twilight zone." Remember the TV program that began with Rod Serling saying, "You're traveling through another dimension - a dimension not only of sight and sound but of mind; a journey into a wondrous land whose boundaries are that of imagination" ? This is what scientists refer to as the first stage of sleep. Sleep researchers, who are much less poetic than Rod Serling, can identify exactly when experimental subjects "fall" asleep - when they leave the world of the awake behind them.
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