I've been deathly ill and confined to my bed for the last week, so it's given me time to reflect upon sleep. Karl Barth described human sleeping as "little images of the great and only uprising of Christ in his resurrection." So, we may reflect upon the revelation of Jesus Christ in his death and resurrection as an image of sleep par excellence so to build a natural theology of sleep upon it in order to understand the common human phenomena of sleep.
The New Testament frequently uses sleep metaphors and it describes death as sleep and resurrection as 'rising up' (as from sleep). Sleeping has two elements—laying down and rising up—and these correspond to the death and resurrection of Jesus. Barth describes sleep as a "little" image because humans do not lie down once and arise forever like Jesus. After awakening, we experience rest for a period of time, but it quickly fades and we are forced to lie down again, and we are enslaved to this cycle for our entire life. Jesus "rose again" from death (as the creeds say) and he entered a rest that was unending (cf. Hebrews 4) and it gives us hope that that all of humanity and the whole world will one day enter the rest of Jesus Christ (cf. Heb 4:8-11, Rom 8:22-24). So whenever we lay down to sleep or arise from sleep, let us remember Jesus has laid down to sleep (in his death) and from it he arose again (in his resurrection), and that he now experiences rest (and eternal life) that we already have in him (John 5:24).
In Karl Barth's commentary on the Apostles' Creed, he wrote "'He rose again.' There are two elements in the term "to rise again": to awake after having slept; to rise up after having lain down. In sleep, we are so to speak, outside ourselves, we do not control our persons. We find ourselves in the unconscious, in dreams, as if in the hands of another power. On awaking, on "rising," we reenter life. This is the formal sense of the word resurrection. But this still is an image of the resurrection. For each of us who rises up will again lie down, and at the end of our lives, everyone of us will lie down. Our uprisings are but little images of the great and only uprising of Christ in his resurrection. We begin in our mother's bosom, and we end up in the bosom of the earth. But there is always this little image: a man rising up, trying to live. But it is a try only. Christ's resurrection, on the contrary, is the resurrection par excellence: Christ rose up out of death, he lives, he stands up he watches, as God himself rises up, without setback, without relapse. There in the Christ risen, lies the truly human reality." 
A theology of sleep is an encouraging reminder of the death and resurrection of Jesus Christ each time we lay down to sleep and when we awaken from it. It is also hope for those that sleep is a time of suffering, as it has been for me the last week, as for all who struggle to sleep well.
1.Barth, Karl. Ed. Jean-Louis Leuba. The Faith of the Church: A Commentary on the Apostle's Creed According to Calvin's Catechism. Trans. Gabriel Vahanian. New York: Meridian, 1963. 106. Print.
2. Header Image Background. Wikipedia: "Jackie Martinez in B & W Sleeping with a book"
Related: Karl Barth, Resurrection, sleep, sleeping, The Faith of the Church, The Faith of the Church: A Commentary on the Apostles' Creed according to Calvin's Catechism, theology of sleep