Diana got that seventh-sense intimation that she had touched on an unmentionable matter; although a strangely involuted one whereby the fact that it … - Adam Roberts

Are we in a dream?" Lebret asked. "Might we actually be dead and in some afterlife?"
"How could we test either supposition?" the scientist asked, with characteristic practical-mindedness. "What conceivable experiment could we design to falsify such a claim?

I have heard the rumours," said the captain, directing his attention to the food on his plate.
"Ah, but rumours," said Lebret easily, "may not be trusted. Appearances, you see, can trump reality.

As far as dreams were concerned—well dreams are generated by the random processes of neural oscillation during the brain’s rest phases. What dreams do is cycle and recycle images and feelings, rationalisations and fears. There’s nothing special about that. It’s not the dreams that matter (chaff, mental turbulence, the rotating metal bars moving endlessly through the transparent tub of metaphorical slushy). It is what the problem-solving circuits in the mind make of the dreams. Dreams iterate and test mental schemas, discarding the maladaptive to return the adaptive to the slush to be reworked. Dreams are emotional preparations for solving problems—that is why we have evolved them, because problem-solving abilities are highly adaptive and thus strongly evolutionarily selected. Dreams intoxicate the individual out of reliance on common sense and preconception, and tempt her into the orbit of private logic. Dreams have utility.