What's So Funny?

Last night it happened again; I think it must have been around five A.M. It's been occurring on and off during the wee hours of the morning for the past year or so. What is it? Laughter. Laughter in my sleep. Late-night, belly-chuckling, pure from-the-heart laughter. I can't remember what the source of humor was last night. All I know is that it was a good one. It starts when I have one of my silly dreams. Or sometimes just a chuckle will get the whole ball rolling. Eventually while doing this I wake myself up.