That’s the Dope in a nutshell. Welcome!
I can understand the “unknowingly lost in a fantasy” meaning, but I wouldn’t use it that way myself. I see it most often as the “stuck in a research chain.”
I, myself, use it more often when discussing movies (etc) to refer the threshold moment where the protagonist(s) are about to hit that point of no return and truly begin their adventure in a different world. I realize that’s kind of literal, but I talk about movies a lot.