[He squeezed her hand lightly as he straightened up to walk with her back to the living room. He'd worry about cleaning the wall later. There... was no real cause to scold a child for something that he could see where she had made the error.

Her question makes him pause as he tries to think how to explain.]

Where I'm from, people don't sleep the same hours all of the time. We have someone who stays up all night [an exaggeration, but it will make his point] to watch out for everyone else while they sleep. I'm used to doing that, so sometimes I get tired during the day.

[Easier than explaining constant worrying and the like.]