The cause and origin of the three states is Atman,which is in the form of consciousness. Atman appears as waking or dream and disappears as deep sleep. Thus it is for the seeker to know what appears as duality (waking or dream)and what disappears as non duality (deep sleep).
The body and the world are exists only in duality (waking or dream). They are non-existent in non duality (deep sleep). To unfold this mystery one has to know what is mind and what is the substance of the mind.
Only in duality (waking or dream) one knows that he exists, in deep sleep the objective existence is absent.
One is aware of his body and sees his body moving and thinking. But he is unaware of the fact that he and his experience of the world are within the experience of duality (waking or dream).
One has to realize the fact that, the body also moving and thinking and being in all sorts of places in the dream while it is actually lying fast asleep. The dream is reality until waking takes place. The waking prevails as reality until the wisdom dawns.