Becoming Derlbert Grady: ALL WORK AND NO PLAY MAKES JACK A DULL BOY

We are near the end. Jack has completely lost his mind, and all he wants to do is murder his family, or anyone that crosses his path while his attempting to.
All the conversations he had with Delbert Grady, are strongly echoing in his head, and we can see and feel how the shadows had taken Jack's sanity. The suffered love, the constant struggle of daily monsters, became insignificant next to his desires of letting all of his frustrations go as he bashes Wendy's brain all over the floor.
The woman in the bathtub, Grady's shade, the barman, the ball, are recurrent visions that Jack is having now, and because he hasn't seen Wendy or spoken to her in a long time, he is losing the little reason he had. Every time she approaches him, he rejects her, and they have reach that point of uncomfortable silences and heavy breathing.

Suddenly, Danny gets wounded by a figure of the room 217, and Wendy blames Jack. We cannot know who harmed him, but logic tells us to suspect of the lying shepherd. Hell breaks lose. Wendy discovers that all Jack has been writing this time, the major masterpiece, is actually a repetition of the same sentence throughout all those sheets: "ALL WORK AND NO PLAY MAKES JACK A DULL BOY". She then realizes how disturbed her husband is, and also how dangerous the whole situation has turned.

Jack stops pretending. He yells at Wendy telling her to remain calm and let him finish talking, and when she does, he smirkingly looks at her and says "Don't be afraid Wendy, I won't hurt you, I'm just  going to bash your brains in. Bash them right the fuck in." Persecution begins, and Wendy manages to lock Jack in the kitchen, and it's a mystery how he escaped from there. Maybe Grady helped him out, maybe.
As soon as he leaves the kitchen, he determines to kill anyone that would dare to walk in front of him, no matter who it might be. Danny hides, Wendy runs, and Halloran, who had just arrived to the hotel to help the boy and his mother, gets hurt by Jack's axe, fortunately, he survives to later help Danny and Wendy escape.
Jack has been possessed by Grady's spirit. That's for sure.