The concept of sleep carries with it the inherent and persistent "I" thought.
The concept of sleep requires an "I" who sleeps, a "ME" that is a body-mind in which limited consciousness stops and starts, a "small self" which becomes unconscious while the world "outside" continues to exist.
There is an appearance of a waking state, an active consciousness, an identified mind where the True Self or Presence is mistaken for the body, a body lost and roaming in a world which appears separate.
This resolves at night as this state changes to a dream world, another seemingly "solid world" where the character is identified with, moves about, thinks, has pleasure and pain, desires and fears.
In the "deep sleep" state - no forms arise, no identifications are possible. Only the pure unidentified consciousness remains.
In reality these three states are only transitory, only flowing perceptions, conceptualized by the waking mind as an "I" who is awake, an "I" who slept, an "I" who was dreaming.
Your true essence, your timeless Beingness, the ever-present Self, was present and remained still and silent, watching without attachment, resistance or conditioning, throughout the changing appearance, throughout the "stages" conceptualized as waking, dreaming and deep sleep.
Something is present, always, to see the passing of the "I" who sleeps. Find out what knows the one who is awake, who dreams, who sleeps. Find out what is knowing the Mind which overflows with the concept of an "I" who is here, separate, awake, dreaming or sleeping.
Don't trust the beliefs of the mind - look within - something is witnessing the thoughts which color the appearance with identification, with an "I" who "sleeps".
Sleep is only a concept, a conceptualization of the appearance and disappearance of identified consciousness, an identification with a body and mind which appears and disappears. Pure Self is that to which these appearances come and go.
No one sleeps.