We exist in deep sleep or dreamless sleep as evidenced by our remembrance of the state during the waking state as when we say “I slept happily”. What also characterizes the dreamless sleep is that we exist during it without being associated with the body and mind. What is our real or true nature should be with us all the time. So, if the body and mind do not exist for us in deep sleep, then body and mind cannot be our real nature or true selves. But what exactly exists during deep sleep. Only pure awareness.