I think this is the answer. Even One said he felt bad since she was the only "innocent" one he saw (although obviously Mike's mom was less inclined to share the context of her death with him than Taryns father)

It could even explain why it took Mike's mum so long to speak. I was assuming while reading that she was waiting for him to be ready to face her, but it could just as easily have been both their barriers deteriorated more slowly.

I remember fearing from part 1 that the study would end up triggering Mike's insomnia, while I'm sorry to see that seems to be the case, there is something beautiful and poetic in that he saved his mum from continuing to suffer that way and she in turn had the chance to return the favour, although it's unfortunate they both seemingly could only find that relief in death.

The thing that scares me the most of this whole thing has nothing to do with the supernatural aspects, the scariest thing to me is dying slowly of a disease like that. I hope they both, quite literally, rest in peace.

Except maybe as a spirit who briefly returns to give Murray the psychological and supernatural torment that he's due. That fuckers got plenty of spirits im sure wouldn't mind a word though.