By the word 'sleep' we understand 'covering of ourselves from the world of which we are conscious.' But we do not realize that when we are awake we are covering ourselves from another world, which is in fact more real. The difference between the sleeping and waking state is that when we cover ourselves from what is real we say, "I am awake," and when we cover ourselves from what is unreal, and illusion, we say we are asleep. It is the self that is covered.