Traumatic events? Hmm...Well, I can't think of anything that happened at night, although, when my dad was alive, he'd drink heavily and yell at and berate my mom during the day. By evening, he'd pass out and my mother and I would wait in my room until he left the living room for his bedroom around ten. This went on since he retired in 1999 until the around the time of his death.

He's been dead for over a year, but maybe, subconsciously, I associate that time of night with tension and anxiety. Very good question and I may have gained some insight answering it!