One can understand easily that the entire waking experience is the same consciousness if he reduces waking experience to dream experience and that to deep sleep.

Deep sleep is said to be causal relation, because every day one goes to sleep and wake up and the whole world is before him again but he is not aware of the fact that he and world are within the waking experience.

In the waking experience the man and world are present, in deep sleep only the formless substance; thus one is not aware of the body and the world.

Soul  is not a state or condition. Man is aware of the dream and deep sleep in the waking experience only.  He thinks he is the experiencer of the three states.  But it is not so. He and his experience of the world is present only in the waking experience. Soul or consciousness  is present always as formless witness of the three states which appear and disappear in succession. The consciousness  is the knower all the three states is itself changeless.

Some people regard dreams as real experiences, most people agree that dream experiences are unreal real.  one has to agree  that dream experiences unreal, but he has to realize  that waking experiences also is unreal. And also all the three states are unreal on the standpoint of the formless witness, which is the soul or consciousness . On the standpoint of soul or consciousness,  the innermost  self, the waking experience is similar to dream i.e. both are unreal, despite the feeling of vivid reality they produce at the time.

One can understand easily that the entire waking experience is the same consciousness if he reduces waking experience to dream experience and that to deep sleep. 

In a dream one may become another personality. What happens? The knowing capacity in him, the soul or consciousness , associates itself for the time being with the new ego and identifies itself with it. But when the dream ends, he wake up and that dream ego disappears and waking ego appears. The one that powers the dream and waking ego is the formless soul or consciousness , the innermost self, the knower of the three states.