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What Are The Five Stages of Sleep & Why is Stage 5 Called Paradox Sleep?
The Beginning of Sleep
You are still fairly awake and aware of your surroundings during the first two stages of sleep each night. The brain produces the smallest and fastest sleep associated brainwaves, called beta waves. The brain begins to produce alpha waves as it gradually starts to get slower and slower. This is the territory that borderlines sleep and wakefulness. The strange pricks of light you see under your eyelids (phoenali) will begin to take on the form of full blown images known as hypnagogic imagery or hypnagogic hallucinations. These can sometimes be very terrifying, if you are still conscious, but most of the time you fall unconscious long before these begin to occur. This is also where strange phenomena like the falling sensation or hearing someone shout your name happen.
One of the strange events that can take place during this stage is the sudden jerk that forces you awake. This is called the myoclonic jerk.
The first stage of sleep, Stage 1, is a very light stage. When you are Stage 1, you can easily be awoken by the sound of even a pin dropping in your room. This period is a transition between completely wakefulness and actual sleep. During this stage, your brain will produce a high amount of theta waves. Theta waves are the slowest form of brain waves. Stage 1 of sleep only lasts five to ten minutes.
The second stage of sleep is Stage 2. During this stage, the brain produces bursts of rapid and rhythmic activity in the brain waves. These bursts of activity are referred to as sleep spindles. During Stage 2, the body temperature decreases and the heart rate starts slowing down. Stage 2 lasts about 20 minutes.
Stage 3 of sleep is also known as delta sleep. This is because very deep, long and slow delta brain waves start emerging during this stage. This stage functions as a transition between the light sleep and the extremely deep sleep.
Stage 4, or delta sleep, is composed of a large amplitude of slow brain waves called delta waves. The deep sleep of Stage 4 lasts about 30 minutes in duration. Bed-wetting and sleepwalking are very likely during the end of Stage 4.
Stage 5 is the stage where most, if not all, dreaming during the night occurs. It is also known as rapid eye movement (or REM) sleep. This stage of sleep is marked by increased respiratory function, rapid eye movement and a spike in brainwave activity. Stage 5 has also been called paradoxical sleep, because muscle are deeply relaxed and even paralyzed while the brain becomes extra active. Due to an increase in brain activity, dreams occur, but all but the involuntary muscles become paralyzed.
To read more about sleep paralysis, click the following link:
Sleep doesn't progress through the stages listed above in the exact sequence. For example, sleep starts with stage 1, then continues to go through stages 2, 3 and also 4. However, after stage 4 is over, it then goes back to stage 3 and then stage 2. After that, it goes back into REM sleep. After REM is over, it's back to stage 2 and then it continues to cycle in this fashion repeatedly throughout the remainder of the night.
Normally, REM sleep starts within 90 minutes of falling asleep. The first session of REM lasts only around 5 minutes, but as the night progresses, the other stages of sleep get shorter and shorter, while REM gets longer and longer. The longest REM sleep gets by the end of the night is about 45 minutes in length.