Why is that?

I had today off from work, WOOHOO! But I have to ask, why is it that on days I don't work I can pop up like toast long before the alarm goes off and be uber productive? For example, this morning I was up, dressed, drinking my coffee, had tidied the house, and was working on projects, all by the time I'm normally dragging into the office. It's not like I hate my job or anything. I mean sure, I can think of a million other things I'd rather do 8 hours a day and be paid for, you know, hobbies, sleeping, reading, things that could make me a hooker if I acutally were paid for them. But still, I just don't get it. Perhaps it's a mental thing? Does anyone else have this problem?