I'm Confused

It is 1:22 A.M. and I am exhausted.
Why is this confusing? Because yesterday at 1:45ish I was laying in my bed trying fall asleep and not feeling tired at all.

Aren't you supposed to want to stay up later on weekends?
I don't get it. I haven't felt dead tired after work any day this week, and now I do?
Does that make sense to any of you? It doesn't to me.