Why the pronomial verb here?

Question

Juan no ha llegado todavía. Igual se ha quedado dormido.Juan hasn't arrived yet. Maybe he overslept.Hi, I’m confused about se ha quedado dormido. The lesson on dormir/dormirse, quedarse dormido says the pronomial means to fall asleep or suddenly fall asleep. Thanks,Shirley.

Accepted Answer

Hola Shirley
In this sentence "quedarse dormido" is translated as "oversleep" because in Spanish this is the most direct way to express this, so the verbal structure quedarse dormido/-a also means "to not wake up on time and stay in bed sleeping". The lesson on dormir/dormirse is not reflecting this possible meaning because it's a bit more specific but I will add a note to the lesson. 
I hope this helped clarify it.
Gracias y saludos
Inma