I don’t know what exactly you are referring to, but the human brain paralyses the voluntary muscles of the body during REM sleep, so that the body doesn’t “act out” dreams. Theories about this phenomenon include natural selection having determined this trait because when human ancestors slept in trees or in areas with high predation rates, sudden movements in sleep rendered them susceptible to death by fall, or by being devoured while unconscious.
As the brain begins to permit voluntary control again during waking, sometimes you can experience a frightful phenomenon wherein you are aware that you are awake, but can’t move a limb by even an inch. It’s called Sleep Paralysis.
Don’t confuse physiology with philosophy and poetry, please. :)