" Dreaming may simply be a by-product of this nightly cerebral housecleaning. As the brain clears wastes and consolidates memories, neural circuits fire randomly, briefly throwing up fragmentary images, a bit like someone jumping between television channels when looking for something to watch. Confronted with this incoherent flow of memories, anxieties, fantasies, suppressed emotions, and the like, the brain possibly tries to make a sensible narrative out of it all, or possibly, because it is itself resting, doesn’t try at all, and just lets the incoherent pulses flow past. That may explain why we generally don’t remember dreams much despite their intensity—because they are not actually meaningful or important. "

― Bill Bryson , The Body: A Guide for Occupants