15 minutes in we hear the father talking to someone, presumably on the phone, about someone who fell down the stairs, hit his head, is ok and didn't even need stitches.
That's the only explanation you'll get for everything that happens afterwards.. The boy feels abandoned by the father - he isn't ok after that fall, after all..did the father even take his son to the ER or just shrug it off? So now we're in the boy's dream and that's why the father is nowhere to be found and the boy can find no way out and nobody to help him, and every scene is symbolic of the fear and isolation the boy is experiencing.
That's the only explanation you'll get for everything that happens afterwards.. The boy feels abandoned by the father - he isn't ok after that fall, after all..did the father even take his son to the ER or just shrug it off? So now we're in the boy's dream and that's why the father is nowhere to be found and the boy can find no way out and nobody to help him, and every scene is symbolic of the fear and isolation the boy is experiencing.