There’s a moment just before you awake when you are neither here nor there, suspended in both space and time, the sleeping mind shifts gears and begins to breathe with vigor once more; that interlude, that gap in reality is where the spirit, the soul, the “I” in “me” decides today’s fate.
If the gears fail to mesh and the clock winds down, we’re no less the loser either way.
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.
Then, there are times when a person just stubbornly refuses to engage...because it's seen as an intrusion.