General Sleep Facts

Sleep is a physiological "need," not an option for humans. There is a 24-hour sleep "quota" which varies across the lifespan. Sleep deprivation is cumulative and cutting one's sleep short by 1-2 hours a night adds up across the course of several nights to produce a significant sleep "debt." The sleep "debt" creates a building sleep pressure across the waking day until the individual is "overwhelmed" and spontaneously falls asleep -- whether that individual is behind the wheel of a car, truck, boat, or airplane, in a classroom, in a boardroom, at the control panel of a nuclear power station, on a 30-foot scaffold, or at the top of a telephone poll.

The point is that we all have a 24-hour sleep "need" and failure to meet that need on a consistent basis will eventually result in inappropriate and uncontrollable microsleeps during the waking day, without exception. Chronic sleep restriction produces mood irritability and an overall energy drain -- motivation is low, reaction time is slow, and the ability to concentrate and process information is impaired. Dull headaches and diffuse muscle aches and pains are not uncommon.

Normal human sleep consists of 5 recognized stages of sleep after the first year of life -- 4 stages of Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) or Dream sleep -- up until old age. The loss of the "deepest" level of NREM delta sleep (stage 4) brings the number of stages in the elderly down to 4. The 4 NREM sleep stages represent increasing levels of sleep depth followed by a period of REM sleep - the fifth stage of sleep. A complete cycle through all five stages is known as a NREM-REM sleep cycle.

The NREM-REM sleep cycle length varies across the lifespan. In neonates the NREM-REM cycle averages 40-50 minutes long, whereas in childhood the NREM-REM cycle may be as long as 120-150 minutes during the first third of the sleep period and then shorten down to 90-110 minutes after the first three hours. The NREM-REM cycle length through adulthood averages 90-100 minutes, but decreases down to 75-90 minutes in the normal elderly.

NREM delta stages 3-4 predominate during the first third of the sleep episode, while REM sleep predominates during the early morning hours in the final third of the sleep episode. Thus, you tend to sleep "deeply" during the first 3 hours of the night, but do most of your dreaming at the end of the night during the early morning hours before waking up for the day. All five sleep stages are normally seen in just the first 2-3 NREM-REM sleep cycles. Although in children, the deep delta sleep stages 3 and 4 reappear at the end of the sleep period due to the maximum amount of delta sleep during this stage of development.

REM periods are initially very brief -- several minutes long - and increase in duration with every successive NREM-REM sleep cycle. So, by the end of the night, REM periods may be 30-45 minutes long. Adults usually have 4-5 NREM-REM sleep cycles a night, whereas, young children will have as many as 7-9 NREM-REM sleep cycles a night due to the much longer duration of their sleep episodes. Normally, you are "paralyzed" during REM sleep except for your eye muscles and small, rapid twitching movements of your fingers and toes, so that you cannot act out your dreams.

The one exception to this normal paralysis during REM sleep occurs in a rare sleep disorder known as the REM Sleep Behavior Disorder which primarily affects men over the age of 60. Patients afflicted with the REM Sleep Behavior Disorder literally act out what are usually very aggressive dream scenarios. The motor activity involves repeated punching and kicking but may also involve more elaborate and complex trunk and limb movements. Physical injury to the patient and/or bedpartner is the major complication of the disorder. BACK TO TOP

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