Why does Vajrayana place great emphasis on the practice of dream yoga? The reason is that, unlike the absolute quietness of death, when we are in deep sleep, even though alaya consciousness and self-grasping are still operating, all other consciousnesses have stopped. It is much easier to realize the nature of mind when undertaking practice during this period.
However, it is very hard for us to return to this state in real life as we have been conditioned to live in a world constructed by sense organs and consciousness, which makes it very difficult for us not to be dictated by our consciousness. For example, when we see something, the information of the object will be transmitted to the mind consciousness to be processed and analyzed, resulting in a conclusion of either good, bad, yes, or no, which will then determine our acceptance or rejection of this object. We hardly ever touch consciousness at the deepest level.
~ Depicted from "THE HANDBOOK FOR LIFE"S JOURNEY : On Death And Rebirth-Understanding Death