Defining dreams as ‘visions during sleep’ may describe what occurs, but this does not explain what they are. Undoubtedly, they are experiences real enough to produce strong psychological and physiological responses in a person. The nightmare, for example, produces the flight or fight mechanism, with its accompanying increase in blood pressure and heart rate, and even sleep-walking, in readiness for physical action. The passionate dream of a lover, renowned for its emotional and biological effects, is a further example, yet these dreams are not reality.
Sometimes events from the previous day are in our thoughts as we drop off to sleep, so not surprisingly these scenes are re-enacted as literal dreams, in the hope of extracting further information from what has already happened. Reliving events in this way has been suggested as a reason for dreaming, but this is only one aspect. The dream reflecting a foreign land the dreamer has never heard of, or the weird and wonderful mansion to which the dreamer returns night after night, demolishes any such simplistic explanation.
Read More: What Are Dreams