Harry Potter had only found solace from his nightmares in the embrace of his wife, who had also been his third cousin. After her death, he was skilled enough in occlumency to control his subconscious mind to avoid them. Who would have thought that mercilessly slaughtering Voldemort's Death Eaters as a teen who had an abusive childhood would give him many sleepless nights? Oh, he didn't regret killing them one bit, especially after seeing their handiwork, or how they would use their money and influence to avoid imprisonment multiple times. But while he was merciless, taking so much life was not something a teen would be able to deal with easily, regardless of reasoning. Once he grew up, however, he had no such problem after slaying his enemies.