Sleep refers to the process wherein the body is in a state where the motor activity and the senses are suspended. Aside from having partial or complete unconsciousness, the voluntary muscles also become inactive. During this process, the body has a chance to rest, repair damages and injuries, as well as control appetite and growth. Getting insufficient sleep is not only harmful for the physical health of a person, but also for his mental health.
There are 5 different stages of sleep, wherein 4 are non-REM and the other one is a REM (Rapid Eye Movement) stage. Sometimes, the waking stage is also considered as the 6th stage of sleep. The Stage 1 which is a non-REM stage is regarded as the transition from wakefulness into sleep. In this stage, there is a slow movement of the eyes and involuntary twitches called hypnic jerks may also occur. This first stage in the cycle only lasts for 5-10 minutes and when a person is awoken during this stage, he will feel like he hasn’t slept at all.
During the Stage 2 or the light sleep stage, the breathing and heart rate of the person becomes slower. Additionally, there is also a decrease in the temperature of the body as a preparation for deep sleep. Stages 3 and 4 or the deep sleep periods, are characterized by a drop in the blood pressure, relaxation of the muscles, and slower breathing. In these stages, hormones are released and energy restoration is taking place.
During the REM stage of sleep, rapid eye movements occur, and the breathing and heart rate increases. Because there is also an increase in brain activity, dreaming takes place during this stage. Generally, non-REM stages last for about 4 to 6 hours a night, while the REM stage only lasts for 2 hours. The whole sleep cycle (Stage 1 to Stage 5) repeats itself 5-6 times a night, where each cycle lasts for about 1 and a half hour.