Like many other ancient cultures, Egyptians belived the universe was predictable, cyclical, and rational. But this "Cosmic" order was never completely safe. Without order, justice, and "ma'at," the world would soon return to chaos, darkness, and disorder. In one myth cycle, Amon-Ra piloted the Sun-Boat in its daily travels across the sky, and at night battled the serpent Apep, who clearly represented the forces of darkness, disorder, destruction, and "dis"-ease.
Link to Apep and other Egyptian gods