Definition
Sleeping in a deep sleep
Also Said As
How People Actually Use It
That one person who sleeps so heavily that NOTHING can wake them up. (Almost like they're dead)
"Person 1: Yeah, nothing could wake you up this morning. You were dead asleep. Person 2: Didn't you throw water on me? When I woke up I was soaked. Person 1: As I said, you were dead asleep. You didn't move an inch when I threw water on you."
Source: Urban Dictionary