You're one of those people who pretends to be cheerful, even when you have a raging hangover, aren't you?
Being cheerful and bubbly in the morning even if you have to fake it for the first few minutes annoys the grouches of the world. Annoying them cheers me up to the point that I no longer have to fake it.
But I am never bubbly around the sleepy. That would be mean.