It's that point in the semester. Too much is going on. I end up running from early morning to late at night, with stuff to do piling up during the week. Stacks of papers to grade, assignments to write, lessons to prepare, quizzes to write, meetings to attend, students to talk to, e-mails to respond to, and supposedly at some point I'll do some research, too.
And when my week finally ends (which is around 8 or so on Thursday night this semester), I feel worn down and can't stand to look at anything anymore. I usually have a light Friday (usually just a meeting or two, respond to a few e-mails, maybe grade or take care of some minor task), then consider Saturday "off". (Of course off time has it's own commitments, like the need to go to the grocery so I have something to eat, do dishes so I have something to eat off of, and do laundry so I don't stink while I teach the next week. But I still have free time, and I enjoy it.)
But then Sunday creeps up, and off we go again. OK, what do I have to have finished for Monday? Then of course Tuesday will come, and... how long until Thursday night again? Thursday nights are really good. At least this semester.