What is the first stage of sleep in which if awakened you will realize that you were asleep ?

Stage 1 is non-rapid eye movement sleep (NREM). It is a  dreamless sleep. When you have settled to sleep and your lamps are closed. When this stage which typically remains among 1 and 10 minutes, you are peacefully asleep, and you can immediately turn to be fully up. Although you are sleeping, you may rise up thinking like you didn’t sleep at all.