Tertullian

It is certain that, from the very beginning of his nature, man was impressed with these instincts (of sleep). (Genesis 2:21). If you receive your instruction from God, (you will find) that the fountain of the human race, Adam, had a taste of drowsiness before having a draught of repose; slept before he laboured, or even before he ate, nay, even before he spoke; in order that men may see that sleep is a natural feature and function, and one which has actually precedence over all the natural faculties. From this primary instance also we are led to trace even then the image of death in sleep. For as Adam was a figure of Christ, Adam's sleep shadowed out the death of Christ, who was to sleep a mortal slumber, that from the wound inflicted on His side might, in like manner (as Eve was formed), be typified the church, the true mother of the living. This is why sleep is so salutary, so rational, and is actually formed into the model of that death which is general and common to the race of man. God, indeed, has willed (and it may be said in passing that He has, generally, in His dispensations brought nothing to pass without such types and shadows) to set before us, in a manner more fully and completely than Plato's example, by daily recurrence the outlines of man's state, especially concerning the beginning and the termination thereof; thus stretching out the hand to help our faith more readily by types and parables, not in words only, but also in things. [Treatise on the Soul 43]