All my life I've been a "night owl," a person who hangs on to the day long after the sun (not to mention most other human beings) has let it go.
I once ran across another night owl's description of his affliction by a similar malady, but his speculation on the origins of the curse did not ring true to me. The author, Stan Goff, described himself as a bad sleeper, and thus he assumed that he clung to wakefulness because he feared the fevered night itself.
I sleep like a rock. It is the day to come that intimidates me, with its clocks and rituals and obligations. In the night we are free to tell the world to go to hell, as long as we can accept the bargain - at sunrise, the world comes back, and brings hell back with her.