A Good Night’s Sleep

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Author: Ron Cridland, MD

Normal Sleep


Many people think that, if they are lucky, they fall quickly into deep sleep, stay there all night long, and wake up refreshed.  We go through 4 to 6 cycles of various levels of sleep, with each cycle lasting about 60 to 90 minutes.  Many of us wake up for a few moments in between cycles 3 or 4 times per night.  Often this is to change positions, and we return to sleep in seconds.  We probably need to be awake for at least 2 to 3 minutes to process the memory of being awake, so many good sleepers do not often recall these awakenings.  


Sleep Stages

We have two basic kinds of sleep: rapid eye movement (REM) sleep and non-REM (NREM) sleep.  REM sleep is where we do our most vivid, “technicolor”, prolonged story line type of dreaming and our eyes move around quite vigorously as if we are watching our dream.  We do dream in all sleep stages although the non-REM dreams tend to be more abstract, less colorful and brief.  NREM sleep is made up of three stages labeled I, II, and III.  The stages of NREM sleep as well as REM are defined by various brain wave characteristics seen on an electroencephalogram (EEG).  

It is interesting that REM sleep EEG looks a lot like a waking EEG but our voluntary muscles are paralyzed so we do not act out our dreams.  There is a condition called REM Sleep Behavior Disorder where the normal paralysis in REM is sometimes lost resulting in parasomnia activity and acting out of dreams.  There is another phenomenon called sleep paralysis which occurs if we wake up suddenly out of REM sleep and are still paralyzed for a few seconds or minutes.  It may be a nightmare that is waking us up and dream content may also carry over as a hallucination into the wakeful state.  The first or second time this happens it can be quite scary because you may be hallucinating that something is in the room with you, but you cannot call out or do anything about it.  Then the next thing you know it is gone and you can move again.

Stage I is really a “pre-sleep” stage where our eyes are closed and slowly moving around under our eyelids, critical thinking is suspended, and we start to “drift off”.  Stage II NREM is considered light sleep.  Stage III is considered deep sleep.  Stage III is also called slow wave sleep (SWS) because the brain waves on the EEG are tall and wide resulting in fewer cycles per second, or “slow waves”.  At one time we also used to score a stage IV sleep.  Stage III was when between 20 and 50% of a 30 second sleep epoch was SWS.  Stage IV was when more than 50% was SWS.  Recent convention has us now combining stage III and IV together as stage III which is our deep, most restorative sleep.


After a few seconds or minutes of Stage I we go into stage II which is really the first true level of sleep.  Even though we are asleep, we are not “unconscious” and are still somewhat aware of our surroundings.  We may hear noises and wake up.  Because we may remember hearing the noise after we wake up, we may think that we were awake the whole time.  If we snore, we may start snoring in this stage.  When our bed partner says, “You’re snoring”, we may wake up and deny that we were even asleep, let alone snoring.  We were in fact asleep enough to perhaps not be beware of our snoring, but alert enough to hear our spouse speak to us.  Some people may spend almost the whole night in this light level of sleep and believe they “did not sleep a wink”.  In fact they did sleep, but may have been aware of something going on in their environment on a number of occasions during the night and thought they were awake in between those occasions as well.  Because their sleep is light, they do not feel rested and assume they did not sleep.  This is a condition called “Sleep State Misperception” and is treated like insomnia.

Normal sleepers will go from Stage II sleep into Stage III after 15 to 20 minutes of Stage II.  Even in deep sleep, Stage III, we are somewhat conscious of our surroundings, although to a much lesser degree than when in Stage II.  We can often respond to our spoken name, but it may take awhile with a few repetitions to respond and wake up.  Some people have an “Arousal Disorder” and cannot fully wake up out of this level of sleep.  They can wake up enough to talk, walk or even eat, but not enough to know what they are doing.  When we monitor their brain waves during this behavior, they are noted to be still asleep.  This is called a Sleep Talking Disorder or Sleep Walking Disorder or Sleep Related Eating Disorder.  Sleep Related Eating Disorder is differentiated from Nocturnal Eating Syndrome where the individual has insomnia and is awake when they are eating.  In this syndrome the individual has become conditioned to associate eating with the ability to return to sleep and thinks they need to eat to go back to sleep.

After 20 to 40 minutes or more of deep, stage III sleep, we may return to stage II sleep.  Sometimes we will wake up briefly to turn over.  Shortly after we have come up from deep sleep and about 90 minutes after we first went to sleep, we enter the first REM period of the night.  The first REM period is usually quite short, often only minutes.  Correspondingly, the first period of Stage III, deep, SWS sleep is relatively long.  As we go through the night, we spend less and less time in deep sleep, and more and more time in light sleep and REM.

Our 24-hour biological rhythm tends to contribute to our greatest propensity for deep sleep at the beginning of the night.  It also makes our greatest propensity for REM sleep in our usual morning time.  That is why if we occasionally stay up later than usual and then sleep in, our sleep quality may not be the same.  By staying up later we may miss some of our best opportunity to get the full amount of deep sleep.  By sleeping in, we get mainly light and REM sleep which is not as refreshing as deep sleep even though we might have slept the same number of hours as usual.  Thus, the saying, “Early to bed, early to rise, makes a man (or woman) healthy, wealthy and wise” (or at least healthier, happier and better able to work and make good decisions), may actually have some biological credibility.

 


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