He thought he felt the ground walls shake and heard something shatter--something big shatter, with giant pieces falling heavily to the earth. They were sounds he'd heard before, which was exactly the reason he didn't react to them. His mind probably pieced this scenario together from fragments of memories, giving him false hope yet again. No one knew where he was, probably assumed he'd somehow gotten back. They weren't looking for him.
Zuko was imaging this.
Letting out a long breath, the prince leaned his head back against the cold wall and looked up at the ceiling, closing his eyes and attempting sleep in attempt to ignore...it all.