When we are looking at a bright light and that bright light is shut off then we see darkness. In reality there is no darkness. If there had not been bright light first there would not be darkness but light; it is the comparison that makes it darkness. Therefore the experience we have in our deep sleep is an experience of a higher and greater nature. It is so fine, so subtle and unusual-our consciousness being accustomed to the rigid experiences of the physical world that the experience we have in that state is too fine to be perceived, too fine to be brought back to the physical world.