I prefer to say that it's all hallucinations so the time... we just happen to like some portion of them.

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In fact [The Bursar] was incurably insane and hallucinated more or less continuously, but by a remarkable stroke of lateral thinking his fellow wizards had reasoned that, in that case, the whole business could be sorted out if only they could find a formula that caused him to hallucinate that he was completely sane.

This had worked well. There had been a few false starts. For several hours, at one point, he had hallucinated that he was a bookcase. But now he was permanently hallucinating that he was a bursar, and that almost made up for the small side-effect that also led him to hallucinate that he could fly.

—The Truth (2000) by Terry Pratchett