Absolutely everything you think about yourself and the universe could be an illusion. As far as you know, you are real and exist in a universe that was born 14 billion years ago and that gave rise to galaxies, stars, the Earth, and finally you. Except, maybe not.
Other explanations for Boltzmann Brains did not require an 'inside-out black hole', for example https://en.wikipedia.org/wiki/Boltzmann_brain, so this inclusion came as a surprise to me. Not sure if it's necessary.
What baffles me about the theory: If it's true, and reality is (mostly, statistically speaking) imagined ... the physical reality could be anything. It could be very different from the reality we live in. But we created our models of the universe in this one reality we know, and the theory of Boltzmann Brains emerged from that.
So based on these physical models we arrive at the idea of BBs. But if this idea is true, the physical reality could be completely different.
Or what do you think?