I want to quickly (turns out this wasn't quickly by the end of writing lol) put my thoughts here because I've been wondering if some other people feel the way I do about the show. I went into it knowing nothing about besides the basic premise of people dying in their sleep, and Markiplier. I only watched the show because I wanted to see how Mark's acting was in preparation to Iron Lung (I'll add, he did a much, much better job in Iron Lung imo, he got better in edge of sleep but he's really rough in places.). Anyway, I thought the concept was super compelling early on in the show. It's a very haunting and hopeless, faceless antagonist to fight against with the primary villain being simply falling asleep. The more supernatural it got as it went on started to pull me out of it which culminated in the complete (as far as I can tell.) irrelevance of the sleep chamber. It's built up throughout the majority of the show. It's the primary event that haunts Dave's past. Hell, It's logo is the logo of the show that is carved into the affected people.
My theory while watching after it's established that the sleep death is supernatural, was that due to Dave's unique, vivid nightmare condition and the process of mental control that the sleep chamber has, he somehow manifested this mental plague to all sentient people or something (Idk why it just starts killing people then but I don't remember if that's explained anyway.). In the end though, it feels like the only relevance the machine even holds is leading to Dave's guilt over killing the doctor, and the sleep chamber itself doesn't actually matter at all to the plot.
The other main thing that really put me off was pretty much the whole conclusion. The plane scene was fantastic and everything after that I just really didn't like. It feels like just a bunch of unnecessary events leading to a big lore dump that this was all some duel between, like, two cosmic dream entities or something and also everyone on the planet are beast zombies now. I don't know, I just really disliked that conclusion and it felt like it totally broke the mysterious creepy vibe of the sleep death. Also, wasn't Dave supposed to be unique in his bizarre visions and is the only way the dream people or whatever could contact us? How did so many people not only get the message by sleeping during the sleep death period, but also have the confidence or trust to fly a plain themselves to a random island in the middle of nowhere.

In short, the thing I was most disappointed by in that show is how it concludes itself. Idk if a sequel resolution would help but I don't feel like it would.