Does the level of awareness of an awakened buddhist also stay the same event when he sleeps?
sleep is a state of body, not a state of mind. If you are asleep your body has shut down the 5 senses, but your mind can still be active (dreaming).


  "As for those delusion-born fevers — burned with which the householder or householder's son would sleep miserably — that delusion has been abandoned by the Tathagata, its root destroyed, made like a palmyra stump, deprived of the conditions of development, not destined for future arising. Therefore he sleeps in ease. - AN 3.34


If you are practicing mindfulness and meditation regularly you can actually stop nightmares from happening by this habit.