I spent this afternoon sleeping because I'll once again be spending the night in the library, this time in preparation for the exam at 9:15 tomorrow morning. I realised over the past few days that I had more energy and better productivity for thinking of ideas when I'd been in the library overnight; rather than lose that momentum by changing my current temporary sleeping pattern, I thought I'd keep it up for another night.
Also, if I've been awake a few hours I'm more productive than if I'd been awake for one or two. I don't want to wake at 7:30 or 8:00 tomorrow and still be sluggish in the exam. At least by my chosen way, I'll be active.