"The events seen in fiction are a dream or hallucination or make-believe or otherwise not really happening" is really
really
really
really
overdone.
No offense, but, yeah. Theories like that about any story really burn my bacon. That's like not even the first room of interpreting stories, it's outside the entire fortress. In the rain. Covered in garbage. That is on fire.
A big one in recent memory is Over The Garden Wall. The ending makes it so easy to just take it that Wirt dreamed everything, because he and Greg wake up in the same pond they fell into between the time they left the real 70s/80s world and found themselves lost in the fairy tale-like Unknown. It's almost right there, it's almost basically spelled out for you that this is what happened. But if you dig deep and assume it wasn't a dream, possibilities open up to explain how not. My understanding of it is that going unconscious in the "real world," coupled with Wirt's despair made them vulnerable enough for The Beast to pull into The Unknown, to do what he does to kids who get truly lost in his forest. And only after Wirt accepted responsibility for Greg and for his own mistakes and displayed any will to learn from those mistakes and get past them, were they able to defeat The Beast, and escape. "That was weird, it must have been a dream" is the lazy way out of thinking about a story. Think deeper. Think, "that happened... but how, and why?"