Since I'm so busy this quarter, it can be very easy for me to forget which day it is (especially since most of my classes are five days a week). This has amusingly trifled with my plans several times, especially yesterday, which felt like a Thursday but was, in fact, a Monday. If you weren't aware of that, congratulations! You're just as busy as I am! :)
Although, I don't think I've ever read a novel where a character honestly thought it was the wrong day. I've heard amusing real-life anecdotes, and I've heard characters complain about how it feels like the wrong day or missed an appointment because they forgot it was on a particular day.
Of course, this may just be one of those things that's amusing in real life and cliche-feeling in novels, since we all live through it so much.
What do you think? Do you have any real-life habits you'd like to see in a novel? Do you ever feel like it's Friday when it's actually Tuesday? (It is Tuesday today, by the way - I checked!)
Good luck on everyone's busy week!