Well Im a fairly big guy and my quad isnt all that heavy so Id probably be able to get out from under it ok.
Ive only ridden one dirtbike in my life and it was an 80cc when I was alot younger. I didnt lay it down or anything but I didnt ride it far.
Ive yet to flip my quad or hurt myself riding it. I just use a decent amount of caution most of the time.