It's not that complex
To me the whole movie was just a big red herring making you believe that there's going to be a great revelation and explanation at the end.
But it cheats you big time and leaves you all wound up but no satisfaction and with a very weak ending that even a 5-year-old could have figured out.
So much mistery and so many details and a great atmosphere with superb editing and all this didn't have anything to do with the actual truth that some bloke was just dreaming up some random stuff while trying to die after an accident.
Yes, I am very disappointed.