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Your Daily Ups and Downs

Keep your green zone, yellow zone, and red zone in mind when you consider your sleep drive. Your green zone is daytime on your body clock. The yellow zone is evening, and the red zone, night. You will feel better and function better if you can work and sleep at times of day the body naturally prefers for these activities.

As hours awake advance from the green zone to the red zone, your sleep drive increases. People also experience ups and downs in alertness that occur on top of this buildup.

Picture your day as a series of hills and valleys. In the first hours after you awaken—the morning, if you sleep at night—your alertness will be high. Due to your body clock, about eight hours after you awaken—mid-afternoon for night-sleepers—alertness dips, but does not stay low. The mid-day decrease in alertness, sometimes called the post-lunch dip, occurs regardless of whether or when you eat lunch. If you need more sleep, this is a good time to nap.

By tuning into your ups and downs in alertness and sleepiness, you can plan your activities in advance. You may want to reserve caffeine for a time when alertness dips, for example.

Most people continue to function well in the yellow zone, even after staying awake for approximately 14 hours. However, after 15 hours or so of wakefulness, the alerting signal tapers off. Once in the red zone, the body clock sends a different signal to promote sleep.