WHAT IS SLEEP PARALYSIS?
When falling asleep or waking up you may have a scary experience. you want to get up, but unable to do it. You cannot move your legs and arms or even scream. It is scary enough that you do not want to go to sleep anymore. This experience, known as sleep paralysis. While harmless, this can be very frightening. Every culture has some sort of story or explanation for the experience. Why does this happen? During normal REM sleep (dreaming cycle) our muscles get paralyzed to not acting out our dream. If we wake up before the REM cycle has finished, we may notice that we cannot move or speak. One of the major causes of sleep paralysis is lack of sleep. sleeping on back position, stress, the use of some medications, and other sleep disorders, such as narcolepsy, may also play a role.
Image is taken from https://nerdist.com/article/sleep-paralysis-hallucinations-animation/