P1. A sleeping person only experiences sleep paralysis during either the process of going to sleep or the process of waking up. But during REM sleep it is an essential factor to inhibit the enactment of dreams. Let me explain.
When a sleeping person enters that phase of sleep called REM (rapid eye movement) sleep, then dreams are likely to occur. The problem is that your brain can’t actually easily tell the difference between acting out things in a dream and acting out things in the real world. That in itself is an important point, since it shows us just how realistic dreams are to the dreamer, since the brain can’t normally tell the difference. So dreams seem to be real.
Under normal circumstances, your brain sends messages in an appropriate way to your muscles to make you run or to lift your arm up or whatever. For example, if you had a dream when you run, your legs would get the brain messages and you would start running actions while lying down in bed, and that would be most unfortunate maybe. So during your REM state, your brain blocks these messages to your muscles by reducing its chemical agents such monoamines as seratonin, melatonin, histamine, etc.
Acting out Dreams
If your were injected with the appropriate chemical agents to inhibit sleep paralysis during REM sleep then you would move your muscles according to your imagined dream movements. Experiments such as this have been done on dogs and cats.
The even more amazing thing about this, especially with cats, is that in un-paralyzed REM sleep, cats behave like cats and seem to be following some sort of dream narrative. So it looks like dreams (for cats at least!) are in fact structured narratives and not just a series of random imaginings.
Incidentally, my own dream experiences also seem like narratives too.
So sleep paralysis is essential for safety purposes during dreams. The lack of muscle tone is so clear that if you were, say, to fall asleep in a chair and your head just lolled then that is not yet the REM sleep state. When muscle tone is lost then the sleeper in the chair simply rolls off on to the floor.
Falling Asleep and Waking Up
As mentioned at the start, sleep paralysis can actually be experienced by sleepers during the transitions between waking and sleeping (Hypnagogia) and between sleeping and waking (Hypnopompia).
In this state the sleeper can find the paralysis distressing, since they can neither move nor speak, and this state can continue from several seconds to several minutes. As a result, panic responses are common.
To make it even more uncomfortable for the sleeper, these sleep paralysis experiences are often accompanied by hallucinations of devils or wild animals or other terrifying visions.
The good news is that no harm will actually come to the sleeper as a result of these unpleasant experiences and they turn out to be simply anxious moments.
We haven’t mentioned it, but in addition to REM dreams, people also have Non-REM dreams. These are less common but the difference between REM and Non-REM dreams may be significant. In REM dreams the mood of the dream seems often rather darker than in Non-REM dreams, also Non-REM dreams are much shorter than REM dreams, and finally, also it seems that the ratio of Non-REM dreams to REM dreams may be important for people suffering from depression. But again the research is not completed as yet.
But the need for sleep paralysis may not be important in Non-REM sleep since it is not so much a simulation of reality but more just considering the problems of the previous day.