The case for staying in bed: It's warm. And comfy. I'd have to find my glasses in the dark. It probably won't seem that funny in the cold light of day anyway.
The case against: You will never remember the idea. It never works.
Curiously I didn't write down last night's idea and yet I did remember it (didn't seem that funny in the cold light of day). Could this be because I also thought, "I could do a blog entry on this cartoonist's dilemma" ? Hmmm.