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Relevant Ted talk: "Your brain hallucinates your conscious reality | Anil Set" https://m.youtube.com/watch?v=lyu7v7nWzfo

Timothy Leary was telling everyone this decades ago, of course.

Crowley also mentioned it, very likely others before them too

Yup, it's also been said (maybe not using the words hallucination), by sages and philosophers in India and Asia for thousands of years now.