Why do shelves often fall during the night?

Question

I was reading this question and ran across something that has occurred to me several times in the past. It may just be that it seems like shelves fall at night a disproportionate amount of the time but from past experience, I have had no less than four shelves fall in multiple locations, all at night. Is there a good reason why shelves appear to fall at night more often than during the day or is it just random chance.