Can you please get over it?
There are movies with no clear ending. It's on purpose. It doesn't mean you don't get it. It doesn't mean you're stupid. It's just how the screenwriter and the director wanted it. That's all. If you don't like it, don't get defensive. Don't feel threatened. Just go watch different type of movies.
The "visions-during-the-moments-before-death" is an old device in both literature and cinemathography. It's just a way of wrapping things up, nothing more. It really doesn't matter whether it's all real or whether they're imagining it. The important stuff comes before, that's what you should concentrate on.
BTW the movie is great.