Sleep Cycles

Some of us may think that all sleep were created equal. There are those who still operate on the assumption that a one-hour nap can make up for lost hours of regular sleep at night. Unfortunately, this is not the case. The quality of your sleep time and the degree by which your body is rejuvenated by it strongly depends on  whether or not it can be considered as complete.

In determining whether your sleep period may be considered as complete, you cannot rely on traditional measurements of time. Some people can feel very rested after 4 hours of sleep whereas others would still feel very tired after 6 hours in bed. The completeness and quality of one’s sleep is actually determined by sleep cycles. For your sleep to be complete and truly relaxing, you must be able to have completed all sleep cycles or stages of sleep. If one fails to enter into the deeper sleep stages, then the quality of his sleep will suffer. To make the most out of your sleep, it helps to become familiar with the different sleep cycles and the ways by which you can facilitate the completeness of your sleep.

There are two basic sleep types or phases of sleep that comprise the complete sleep cycle. The first one is called the non-rapid eye movement (NREM) sleep, and the second type is referred to as Rapid Eye Movement (REM) sleep. NREM sleep pertains to those stages of sleep where there is low brain activity and no rapid eye movement. It comprises a large chunk of the entire sleep cycle and is further subdivided into three stages.

NREM 1 or drowsy sleep. This stage signals the onset of sleep and is characterized by the early transition from a wakeful state to somnolence or near-sleep. When you’re in this stage, you may consider yourself as half asleep, with your consciousness straddling between the wakeful state and the sleep state. You can easily be awaken or startled by sudden sounds and movement during this stage due to the fact that you are still moderately aware of your external environment at this stage. In some instances when the environment or circumstances are not conducive to restful sleep, a person can remain in this stage for the entirety of the sleep period, resulting in restlessness and a general feeling of not having slept at all. Given the right circumstances, this period will generally last about ten minutes for most people before they fall into intermediate and deep sleep.

NREM 2 or intermediate sleep. When you enter the second stage of NREM sleep also known as “intermediate sleep,” you will gradually lose awareness of your external environment. Your body will enter a rested state and involuntary bodily functions such as breathing and cardiac activity will slow down. For reasons that are still being studied, the brain activity during this period is distinctly characterized by what is referred to as “sleep spindles” which indicate sudden bursts of brain activity.  One may still be awakened by sounds and movement in the external environment, but your tendency to be awakened by these external stimuli will decrease as you sink deeper into sleep. This stage usually lasts about twenty minutes, although you can revert back to this stage several times during a single sleep period.

NREM 3 or deep sleep. The third stage of NREM sleep accounts for the greatest benefit to your mental and physical health. Deep sleep occurs around thirty to forty minutes after you first fall asleep, and it is during this stage that your body is at its most restful state. Brain activity is very low and it is most difficult for you to be woken up while you are in this sleep stage.  This stage was previously divided into NREM 3 and NREM 4. But since both stages were characterized by the occurrence of slow waves of brain activity referred to as “delta waves”, the two stages were recently reclassified into a single stage. Dreaming has been noted to sometimes occur during this stage, although it does not occur as frequently as when one is in REM sleep. It is also during this period that parasomnias or sleep disorders such as sleepwalking and teeth grinding occur.

REM sleep. Rapid eye movement sleep refers to the stage during your sleep period wherein brain activity spikes up and dreaming frequently occurs. This stage may be distinguished from the earlier stages of NREM sleep by the sudden rise in brain activity and noticeable increases in some involuntary bodily functions such as cardiac activity and blood pressure. As may be inferred from the name itself, this stage can also be identified through the occurrence of rapid eye movements while asleep. When you are in this stage of sleep, an observer may easily note the rapid movements of your eyes which indicate the occurrence of dreaming.

You are oblivious to the external environment while in the REM stage of your sleep cycle, and your body may not register any physical pain when it accidentally hits objects while acting out your dreams. This may explain your complete lack of any recollection of pain when you find yourself waking up on the floor one morning with minor bruises or a noticeable bump on the head. The REM stage usually makes up for around 20-25% of your entire sleep period and can normally occur 4-6 times during a single sleep period. It generally occurs at the latter part of your sleep, and if awoken during this stage, you may find yourself still having clear recollections of your most recent dream.