What Is A Sleep Cycle?
Sleeping is not a linear process. Instead, it involves swinging and oscillating between various sleep cycles. Our mind goes through various phases as we sleep. The oscillation from one phase to another is known as a sleep cycle.
Sleep can roughly be divided into two categories – REM sleep and NREM sleep. REM means Rapid Eye Movement and NREM stands for Non-Rapid Eye Movement. The NREM stage is the dreamless stage whereas we have dreams during the REM phase. The NREM phase has around three stages immediately followed by the REM phase. One oscillation between these phases completes one Sleep Cycle.
A single person begins a new sleep cycle every two hours i.e. 120 minutes. This means that during one long period of unbroken sleep, one is likely to go through roughly four or five sleep cycles. One does not sleep very deeply through all phases of the sleep cycle. Instead, it tends to oscillates from light to heavy to a dreamy nap
Stage 1 Of Sleep Cycle
This is the first stage of the NREM phase. This is the phase of very light sleep. This sleep state is very easily disrupted by sudden changes in the environment thereby activating the brain. It is characterised by slow eye and muscle movements. The body is relaxed and brain activity starts decreasing. Some people may experience muscle spasms or hypnic jerks or even have dreams of falling during this initial stage.
The Second Stage
Under the NREM phase, this stage is considered to be the first actual stage of sleep. At this stage, along with the slowing eye movements and muscle relaxation, the body temperature begins to go down. The heart rate also slows down significantly and one cannot be easily woken up from sleep. Furthermore, brain waves now make sleep spindles and K Complexes. Both of these are considered as a guard for the brain from waking up.
The Third Stage: NREM
This is the phase of deep sleep in the NREM stage. Here brain waves slow down considerably and people waking up at this stage is very rare. Common problems like sleepwalking or sleepwalking or night terrors and sleep paralysis all occur at this stage. This is effectively the deepest phase and is the last stage of the NREM cycle before the REM cycle sets in.
The REM Stage
This is the last and final stage. The full form of REM is Rapid Eye Movement. This is the stage where we have dreams. During this stage, eye movements are rapid and brain waves get activated. Usually, one can easily be woken up during the REM stage. Waking up at this stage always makes people feel disoriented and/or very sleepy.
It must be noted that the movement from deep sleep to REM sleep is not a sudden, abrupt movement. Rather, the sleep cycle moves from light to deep one and then back to light and finally ending in the REM stage before the setting in of the next cycle. Typically, an adult goes through roughly five sleep circles at night. Children require more.