When man wants to sleep, the soul, being the life of the flesh-body, must, before man can fall asleep, withdraw and come out of the body; for as long as the soul dwells in the whole body, the body cannot fall asleep, because the sleep of the body is nothing else but the soul coming out of the body, which is the life of the body itself, because the body is dead matter animated by the soul.
Source: The Soul - dictated to Franz Schumi