Is it all in the woman's head or is it supernatural or both?
At first, it seems like her lack of sleep due to overwhelming grief and everything else, and the sudden appearance of the book has made her obsess over something she may have created herself without knowing it, and I was quite happy with the idea that the Babadook is just a waking nightmare for her in her addled mind, since it seems the boy can't see it, but now I'm wondering: Did she make the book in the first place, or was basically the Babadook itself and how it arrived? I thought it was all in her head, as I said, but then we have the boy seeing it too, in the car (unless it was a brain fart as well as an overheat due to his wild imagination) but what got me was what caused the boy, in the near climax, to slam against the wall twice and get yanked up the stairs - the Babadook itself, right?
I'm thinking now it's both a supernatural entity that feeds off the woman's poor mental state, and I suppose what it's after is to drive her mad, but in the end, she regains control due to her finally accepting her loss and reinforcing her love for her son, leading to the Babadook being subdued and fleeing to the basement, where she feeds it worms on a regular basis despite it trying to attack her mentally again. Is this how it is?
Why are you here if you haven't seen the movie yet?