According to contemporary teacher Chögyal Namkhai Norbu, in Dzogchen the perceived reality is considered to be unreal. All appearances perceived during the whole life of an individual through all senses, including sounds, smells, tastes and tactile sensations in their totality are like a big dream. It is claimed that on careful examination the dream of life and regular nightly dreams are not very different, and that in their essential nature there is no difference between them.

The non-essential difference between our dreaming state and our ordinary waking experience is that the latter is more concrete and linked with our attachment; the dreaming is slightly detached.

Also according to this teaching, there is a correspondence between the states of sleep and dream and our experiences when we die. After experiences of intermediate state of bardo an individual comes out of it, a new karmic illusion is created and another existence begins. This is how transmigration happens.

One aim of dream practice is to realize during a dream that one is dreaming. One can then dream with lucidity and do all sorts of things, such as go to different places, talk to people, fly and so forth. It is also possible to do different yogic practices while dreaming (usually such yogic practices one does in waking state). In this way the yogi can have a very strong experience and with this comes understanding of the dream-like nature of daily life. This is very relevant to diminishing attachments, because they are based on strong beliefs that life's perceptions and objects are real and, as a consequence, important. If one really understands what Buddha Shakyamuni meant when he said that everything is unreal or of the nature of shunyata, then one can diminish attachments and tensions.

The teacher gives advice, that the realization that the life is only a big dream can help us finally liberate ourselves from the chains of emotions, attachments, and ego and then we have the possibility of ultimately becoming enlightened.

Dzogchen - Wikipedia