Tertullian

We hold the soul to be perennially active because of its continual movement, which is a sign both of its divinity and its immortality. So, then, when rest comes—rest, that special comfort of bodies—the soul disdains an idleness that is alien to its nature and, deprived of the faculties of the body, makes use of its own. This power we call ecstasy. This occurs when we are deprived of the activity of the senses. Lacking sensory input the soul reflects conditions akin to delirium. Thus, in the beginning, sleep was preceded by ecstasy, as we read: "God sent an ecstasy upon Adam, and he slept." Sleep brought rest to the body, but ecstasy came over the soul and prevented it from resting, and from that time this combination constitutes the natural and normal form of the dream.