It has been years since I last read it. Basically a disease that causes nightmares and sleepiness that once you sucomb sends you to your first "trial". If you survive then you gain power but if you die you become the nightmare monster you needed to overcome, harder it is the stronger the power. Then there is like second, third and fourth nightmares if I remember correctly. Each gives you a new harder trial, sometimes with more ppl and the more you survive the higher you go. Is crazy difficult and the dude is just a psycho sometimes, but that is what is necessary to survive.
There is lore from the nightmares too cause there is always some ancient mystery being uncovered every trial they enter.
A lot die obviously and some deaths are just so gorey, really hope they add in a few cause I felt some of them.

Novel readers, what is the story about? I will probably end up reading it cause there's overflowing positive reviews about it everywhere. I just want to know like the gist of it before reading it!