It is especially important for busy students to grant themselves enough time to sleep because one of sleep's most important functions is to stimulate the regions of the human brain that are employed in learning and memory. This important function does not take place until the fifth stage of sleep, called REM sleep, which occurs approximately once at the end of each hour and a half cycle. What's more, each new REM stage lasts longer than the one before, making it that much more essential to the processing and storage of new information.

During this time, the brain processes, consolidates, and synthesizes information learned throughout the previous day, develops connections among memory-strengthening neurons, and replenishes its store of neurotransmitters. Past studies have determined that when deprived of REM sleep after learning a new skill subjects were not able to recall what they'd learned, while subjects deprived of either of the other four sleep stages were able to recall the skill just fine - thus demonstrating that REM is the most important of all the stages of sleep, particularly when it comes to learning and memory. Yet it is the first stage that is sacrificed when sleep is cut short. Since the REM cycles are longest in the morning (or toward the end of the body's natural series of sleep cycles), sacrificing an hour or thirty minutes of sleep in the morning cut into the most important phase of the entire night - the final REM cycle.

Although napping is no substitute for a good night's sleep, it is nevertheless beneficial to keep REM cycles in mind when planning to doze for just a short while. Planning nap-times in increments of 90-minutes most enables sleepers to awaken feeling refreshed because it takes about that long to complete one full cycle of all five stages of sleep. Furthermore, since the third and fourth stages, just before REM, necessitate the deepest sleep, awakening in the middle of such a 90 minute cycle presents the risk of rising feeling even worse than when you lied down.

Those stages are most difficult to awake from, so when you force it when an electric or human alarm clock, grogginess is inevitable. Therefore, an hour and a half or three hour long nap are both more refreshing than a two or four hour nap. This is also important to bear in mind when planning your sleep for the night. Setting your alarm for a time likely to sound in the middle of stages three or four means you're either not likely to hear the alarm or even realize if you hit the snooze or off button - or that if you do awaken, you won't feel as though you've had a very good night's sleep.

Unfortunately, a sleep debt is not reduced by sleeping in on the weekend, or getting to sleep earlier one night to make up for a series of sleep-deprived nights that preceded it.

The only remedy is simply to regularly and consistently give your body the amount of sleep it requires to function optimally. For most people, this means between 8-10 hours of sleep. Although one study determined that a rare gene exists that enables some small, but lucky amount of people to thrive maximally on only 6 hours each night.