When the war comes to Wiesel’s world, his visions change. The night is the only time when people feel calm and quiet; daytime and dark time switch their places. Wiesel talks about night events only because all the things that happen during the afternoon are the same. The darkness brings changes to their lives; thus, he compares the world to nightmares.
Detailed answer:
In Auschwitz, Wiesel was separated from his mother. He sees all the murders and corpses and compares this to a nightmare. The world around him seems to be delusional. Wiesel cannot understand why someone wants to kill women, men, and children. This new reality does not fit his virtuous and all-forgiving worldview.
The dreadful scenes of fire and death of innocent people kill his God and his soul. Wiesel seems to meet the Angel of Death and is about to see Hell. The new world has no time anymore. Nighttime would come every day, and the Jews would be afraid if they would live to go through the night. Therefore, everything terrifying is delusional as in a dream.
After some time, Wiesel realizes that he is not afraid anymore. There is nothing to be fearful about because dreams cannot be real. However, there is one thing that still frightens everyone: the word “chimney.” It is the only realistic part of this delusional world because the boy sees the flames and smells the smoke. Wiesel understands that everything will finish: the Hell will disappear, the nightmare will pass. The only things that will stay are Wiesel’s memories about these events.