"Nightmare" is a work on memory.
Remember of those who lived the war and the anxiety of those who dread her. The unconscious is marked for ever by this violence, nightmares will be frequent.
Memory as duty also because when the war is far, , it seems to be not real, as a virtuality, and some are tempted to forget all the horror, as they invite the refugees to return to their country at war.
The upper layer show an imaginary perception today. The lower level show how was the reality in the past.