"Are you okay?"
"Yeah, I'm just tired."
The perfect excuse.
I've been a little overly lethargic lately, come to think of it. I don't mind being tired. Being in a constant dream-like state is a-ok by me. I tend to be less afraid of myself when I'm tired, because frankly, I don't care.
And, on days that I've been exhausted, I tend to learn a lesson of some kind. Something very good, very strange, or very bad happens. But I'm never left wanting in the end.