There is only one state, that of consciousness or awareness in existence. The three states waking, dream, and sleep cannot be real. they come and go but real will always exist. by long habit, we have been regarding the three states as real. we call the state of mere awareness, the fourth, turiya meaning of turiya is beyond three modes as called in Vadantaic vocabulary it is the name of our self. —- Maharishi Ramana.
Comments; Our self is one which is the union of the whole of the world. now on awareness ( consciousness) three mods as waking, dream, and deep sleep happen. it is like figures of a screen. pictures are changing, in movies, there are so many happenings in pictures as happiness, sadness, but screen of the cinema remains the same. like this, on sakhsi ( Observer) three stages come and goes, but our self ( witnessing,). by self-inquiry, we come to know our real being which is not changeable but it is blissful.