Different levels of awareness exist. Every instant, a certain separation divides what you think, feel and physically do. Your being has too many functions for the human mind to keep track of all at once. The more aware you become of this separation, the more you may begin to believe parts of you are dreaming while other parts are more conscious and aware.
If you assume that part of you works while part of you sleeps, then you may begin to believe you can fall asleep and still maintain consciousness. This does not make it advisable to drive or operate machinery as an experiment while you take a power nap. And yet, how you view rest may never be the same. How you sense spatial awareness will also evolve.
It is useful to decide on something you would like to do in waking life or presumed sleep. Otherwise, you have no point of reference. In the case that you choose not to be aware, you selectively tune in or out of internal and external realities. Your underlying motivation shapes the roles you choose to play.
In my experience, conscious participation expands how one explores different levels of awareness. From the moment you take responsibility for perception and formulate deliberate intentions, your life experience changes in degree. You perform roles of observer and participant. You are in your life, not of it.