Understanding What Happens During Sleep

Rest is important. Resting lets the body heal and recover. We need deep restorative rest and sleep in order to develop resilience.
In this blog post, I’m going to cover what happens during sleep. Understanding sleep as a bodily function gives us insight into any barriers to resting and recovering from the daily traumas of life. The prevalence of insomnia disorder is approximately 10-20%, with approximately 50% having a chronic course1. Insomnia requires a holistic approach. In traditional medical practice we are accustomed to prescribing a medication with the hopes of immediate induction of sleep. Short term this will work, but unless we go deeper, start asking more questions, we don’t get to the root cause of insomnia. Medical research has shown that the best treatment for insomnia is behavioral treatment. The American College of Physicians recommends that all adult patients receive cognitive behavioral therapy for insomnia (CBT-I), as the initial treatment for chronic insomnia disorder2. Furthermore, “many medications used regularly and long term for insomnia disorders have an FDA indication only for short-term, as-needed use, in part because hypnotics are associated with dementia, fracture, major injuries, and possibly cancer”3.

Sleep follows a pattern that starts from being awake to deep sleep. Let’s journey through the sleep process from the most wakeful state to the deep sleep.  I feel that in order to improve your rest you should have an understanding of what happens when you are resting.

The Awake Brain

During the day, your brain is in its full functional state. Your sensory organs are fully engaged, allowing for sight, hearing, touch, taste and scent. Your eyes will operate normally, and your blink reflex (the response to a fast moving object coming towards your face) is active. You are also in complete control of your motor cortex, so you have full control of your muscles, allowing for normal movements. Your reflexes operate normally. One example, which is the blink reflex, operates normally during the awake cycle. If an object is coming towards your face rapidly you will blink involuntarily.

Your cardiovascular and respiratory system will typically work automatically. The heart and lungs will take information from the vagus nerve about what is going on in the body. Both organs will also have their own monitoring of the blood in the form of oxygen levels, carbon dioxide levels, and other information to adjust how fast the heart will beat and how rapidly the lungs will respirate. You can override the automatic breathing cycle yourself by doing something like meditation or breath holding.

During the awake state, your digestive system is ready to work, and particularly during the day hours the stomach, small intestines, and colon work in coordination to digest for and extract nutrients as well as eliminate waste. 

It is important to understand that what happens to your mind and body during that will determine your quality of sleep that night.  If your brain has been in a constant state of hyperalertness, or stress, you will likely notice trouble initiating the next step in sleep, drowsiness.  If your mind has been holding on to thoughts of worry, and constantly recycling these thoughts, this may disrupt the relaxation that is needed to initiate restorative sleep. The pineal gland which produces melatonin has a connection with the optic nerves. if there is a constant source of light hitting the optic nerves well into the evening this will suppress the production of melatonin thus the connection with excessive screen time and insomnia. Melatonin production actually begins fairly early in the day but gradually increases in the evening hitting a high point before we hit the next stage which is drowsiness.

The Drowsy Brain

Drowsiness is the gradual development that we associate with starting to feel sleepy. You begin to register the sensation of feeling sleepy when your blood pressure begins to drop.  Your heart rate will also begin to slow down.  Your ability to form new memories decreases, and any new information that reaches your brain will not be stored. The electrical activity in your brain begins to change as well which can be seen on an EEG.  This corresponds to an alteration in your eyes, which will start an automatic slow back and forth movement.  Drowsiness requires a state of deep relaxation.  If something disrupts the drowsy states, the onset of sleep may be delayed or completely aborted.

Light Sleep

Light sleep will follow drowsiness.  The electrical activity of the brain will continue to change, reflecting lower amplitude of activity on EEG’s.  The eyes will stop moving at this point, tending to stay in oe place.  Breathing is now automatic and no longer under the control of the conscious brain.  When you’re awake, if you hold your breath, you will get a strong urge to breathe within a few seconds due to your body’s mechanism to respond to elevated carbon dioxide levels in the bloodstream.  In Light Sleep, your body may not respond to breath holding.  Individuals suffering from sleep disorders, such as sleep apnea  may have prolonged periods of breath holding in light sleep and not wake up.   Roughly half of the night will be spent in Light Sleep.

Deep Sleep

In the Deep Sleep stage, brain activity continues to slow even more.   Your brain will cycle between light sleep and deep sleep several times throughout the night.  The body is even less responsive to rises in carbon dioxide in the bloodstream.  The conscious brain’s control of the body has been released.  Dreaming does not occur yet.  Deep sleep sets the stage for the most important portion of the sleep session, REM sleep.

REM Sleep

REM, or Rapid Eye Movement, is the necessary sleep stage that allows for true rest. It is during this phase that the voluntary control over your muscles is no longer present; This is the stage of sleep when dreams occur. Voluntary control over your muscles or your breathing. So you are in a way paralyzed. Many individuals describe an event of waking up from a deep sleep being completely paralyzed. This phenomenon is believed to occur during REM sleep. Likely the brain is aroused for some reason but the body remains paralyzed. There is enough consciousness that the person is aware that they are unable to move their body. when I’ve discussed this event with patients almost all of them return to some form of sleep after it has happened.

Waking Up

After going through several cycles of sleep throughout a night, your body will prepare to wakes itself.  In the early morning hours, your blood sugar will rise.  This effect can become exaggerated in diabetics, leading to the Dawn Phenomenon, or early morning high blood sugars despite being in a fasting state.  Your cardiovascular system will prepare to become upright by causing a rise in the pulse and blood pressure. In individuals with high blood pressure, this natural process may be exaggerated, leading to very high blood pressures upon waking up in the morning.. Those individuals may know very high readings when they first wake up in the morning. The endocrine system also becomes very busy in the early morning hours. The adrenal glands begin to produce higher levels of cortisol preparing the body to become more alert.

Sleeping is a complex process, and as you can see, there are many steps in the process to ensure a good night’s sleep. It is easy to take the process of sleep for granted. Understanding that sleep is a complex biological process that requires the coordination of multiple systems in the body helps us to realize how insomnia occurs so easily.

  1. Buysse DJ.   Insomnia. JAMA. 2013 Feb 20;309(7):706-16. doi: 10.1001/jama.2013.193. Review.
  2. Qaseem, A., Kansagara, D., Forciea, M. A., Cooke, M., & Denberg, T. D. (2016). Management of Chronic Insomnia Disorder in Adults: A Clinical Practice Guideline From the American College of Physicians. Annals of Internal Medicine,165(2), 125. doi:10.7326/m15-2175
  3.  Wilt, T. J. (n.d.). Pharmacologic Treatment of Insomnia Disorder. Annals of Internal Medicine.

2 thoughts on “Understanding What Happens During Sleep”

  1. Thank you for this explanation! I have found that when I do my meditations in the evening and this has just been a game changer for me and my sleep patterns. I’ve been able to have deep sleep and not wake up until sunrise! Thank you for the sleep activity breakdown!

    1. Thank you for your comment! Sleeping is complex, and when we breakdown what happens before and during sleep, we can see how activities like meditation improve sleep quality and quantity.

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