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Definitions || What is Normal Sleep?

Happy New Year! I hope that, among your personal resolutions for 2015, you’ve thought about adding “more and better sleep” to the list. Sleep is not an optional process, after all; you can only replace lost sleep with found sleep. And if you don’t, you accrue sleep debt that, over time, can have a detrimental effect on your ability to do just about anything.

Yawning Newborn Baby
[public domain image]

The vast majority of people in the US (all ages, all genders, all races) do not sleep well or for long enough, and new research in sleep medicine shows that this has a whole-body impact that can aggravate or even lead to other chronic illnesses like heart disease, diabetes and neurological disorders. When one considers that lack of sleep can lead to dangerous behaviors like drowsy driving, it’s not a stretch to suggest that poor sleep has silently become both a public health and public safety crisis in this country.

Fortunately, many sleep-related problems and disorders can be prevented or treated easily with lifestyle changes, simple therapies, improved breathing devices and new classes of medications.

But how do you know if your sleeping life is problematic for you? It can be hard to know if you have apnea, for instance, if you do not have a bed partner witnessing you asleep and gasping for air. Lots of people sleep all night but, because they sleep in fragments (unknowingly), they do not wake up feeling refreshed and alert. Maybe it seems normal for some to take a long time to fall asleep, while others insist they can “get by” on 6 or less hours of sleep. But the facts bear out that none of these experiences or conditions can really be described as a normal part of the sleeping process.

In order to know what could be abnormal about sleep, it’s probably best to start with an understanding of what’s normal. Here are some basic notions about what NORMAL sleep resembles.

  • The definition of sleep is not just “not awake.” Sleep is “a physiologic state characterized by decreased consciousness, metabolism and movement.” Sleep is not a state of unconsciousness, by the way. Your brain is quite active while you sleep; you just don’t have any awareness of all the electrical and chemical activity taking place in your brain (Spriggs, 2010).
  • Most people need to sleep around 8 hours a night. That may seem like a lot in our time-pressed world, but the fact is we are generally “entrained” (or matched) to a circadian system that ties in closely with the day and night cycles of the earth. Our circadian systems effectively shift into sleep mode by way of chemical and neurological processes that require sleeping for about 8 hours.  It’s normal to sleep, in other words.
  • Several factors affect your ability to sleep. Light (or lack thereof) is perhaps the most effective influence over sleep cycles, but other factors include body and room temperature, eating habits, drug use (even legal and prescribed) and your daily level and timing of physical activity. 
  • Sleep is ruled by a complicated network of systems inside the brain which regulate sensory information, body temperature, breathing, blood pressure, alertness and sleep drive. It’s not just the body shutting down; in fact, it’s quite the opposite.
  • The body has a sleep drive, which is similar to a sex drive or a thirst or hunger drive. Basically, your body develops pressure to sleep during the day’s deprivation of sleep. The more awake you are over a long period of time, the higher your drive to sleep will become (this is a simplification of a more complex process, but I think you get the picture).
  • There are two states of sleep: REM and NREM sleep. REM stands for “rapid eye movement” sleep and indicates when the brain has reached a stage of sleep in which body processes shift and the brain becomes as active as if it were awake. The eyes dart back and before beneath the eyelids; this is the stage where most dreaming takes place. REM sleep is the stage when the brain is in recovery mode, healing and repairing itself after a long day of hard work. NREM, or Non-REM sleep, generally leads up to and away from REM sleep. There are 3 stages of NREM: stage N1 transitions from wakefulness to stage N2 sleep, which shows signs of neurological and physiological shifts which represent the body falling to sleep. Stage N3 is the deepest, dreamless phase of sleep which helps aid the body in recovering from the physical stresses of the day.
  • Periods of REM and NREM alternate as we sleep in cycles that last about 90 minutes each.
  • Sleep efficiency is a way to measure how much sleep you actually experience while in bed. Normal sleep efficiency is around 90% of total sleep time. In other words, if you are in bed for 8 hours, you would have a normal sleep efficiency if you slept at least 7 hours and 12 minutes of that 8-hour period. Not surprisingly, an insomniac will have a lower rate of sleep efficiency, as they are in bed for quite a while before they fall asleep, or they may waken early and never return to sleep, or they might experience both problems. 
  • Related to sleep efficiency is sleep latency, which is the measure of how long it takes to fall asleep (the point of sleep onset). Most people take anywhere from 5 to 20 minutes to fall asleep (or to return to sleep after waking in the middle of the night).
  • One’s ability to sleep is affected by body chemistry (hormone changes, in particular) as well as by sleeping environment (how light, how quiet, how comfortable, etc.) and other physiological factors (like chronic pain or allergies). 
  • One’s ability to wake up is also affected by similar factors. New mothers know very much how easy it is to awaken upon the sound of their crying baby. This has a hormonal component as well as a physiological one and is quite normal. 
  • An occasional awakening at night to use the bathroom or get a drink of water isn’t abnormal, but regular and/or multiple awakenings every night might suggest something is amiss.
  • Other things to know about normal sleep:
  • You don’t have to lie down or even shut your eyes to fall asleep. 
  • Your body typically undergoes a sensory blunting and almost complete paralysis as part of the normal sleeping process (specifically, during REM sleep).
  • Memory consolidation is one of the key activities that takes place while you sleep.
  • Dreaming is a normal function of sleep.

Understanding what comprises normal sleep is key to recognizing when one’s sleep processes or habits aren’t in balance. Awareness makes all the difference in the world. If you aren’t feeling rested every morning when you wake up, it’s high time you found out why. Chances are good it’ll be an easy fix and then you can move on, with more energy and better health.

Reference
Spriggs, WH. (2010). Essentials of Polysomnography. Sudbury, MA: Jones and Bartlett Publishers.

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2 Comments on Definitions || What is Normal Sleep?

  1. At what stage of sleep does sleepwalking occur?

  2. At what stage of sleep does sleepwalking occur?

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