Some animals are designed to be nocturnal and stay up all
night, sleeping throughout the day. While humans can technically go to sleep
whenever they want to, our bodies are made to sleep during the night. Human
beings also have a natural sleep pattern that involves regular intervals of
sleepiness during the day.
How Your Internal Biological Clock Works
Each person has a circadian clock that regulates wakefulness
and sleepiness throughout the day. In general, an adult’s strongest need for
sleep occurs between 2:00 to 4:00 in the morning and 1:00 to 3:00 in the
afternoon. There are some variations between individuals, but these sleep times
are generally true for most people. When someone gets enough sleep, their daily
dips in energy levels become less intense.
The circadian rhythm is driven by a section of the
hypothalamus known as the suprachiasmatic nucleus (SCN). This section of the
brain responds to levels of light. The optic nerve in the eye tells the SCN
when it is daylight or nighttime. Then, the SCN tells the brain to adjust for
sleep or wakefulness. Things like jet lag can end up harming your natural sleep
The Stages of Sleep
A natural sleep pattern involves four stages of sleep called
one, two, three and rapid eye movement (REM) sleep. People cycle from stage one
to REM sleep multiple times during the night. Each of these cycles can take 90
to 110 minutes to complete.
Stage one is the lightest stage of sleep. Your muscles and
brain waves start to relax. Many people experience sudden muscle spasms as they
drift into stage one sleep, and it is fairly easy to wake someone up during
Stage two is where “true sleep” begins. Your brain waves
slow down, and your eyes stop rolling. It is much harder to wake someone up
during this stage because structures called K complexes and sleep spindles
protect your brain from waking up. In this stage, your heart rate and body
temperature start to decline.
Next, people enter a deep sleep in stage three. This is the
restorative sleep that helps you feel rested the next morning. It is extremely
difficult to wake anyone up during this stage. If someone is prone to night
terrors, sleep talking or sleepwalking, it generally happens in this stage.
REM Sleep and Sleep Apnea
The final stage is called REM sleep. In this stage, your
eyes move rapidly from side to side. During this natural part of the sleep
cycle, you experience dreams. Your brain waves are more active than they are in
stage two and stage three, which is one of the reasons why it is easier to wake
up in this stage. If you do wake up during this time, you will most likely feel
drowsy or groggy.
REM sleep is the stage where sleep apnea is most disruptive,
and certain patients only have disrupted sleep during this stage. It’s also the
stage where the use of CPAP
machines for individuals with sleep apnea is especially important. Studies
have shown that disruption during REM sleep lead
to decreased performance and memory as well as other negative side effects
throughout the day.