Week 47 - A tenebrous pony
Celestia seems like a character that would be prone to fits of melancholy and depression. She is well over a thousand so she has watched almost every pony she ever cared for die. Also her daily routine really only requires that she raise and lower the sun, eat, sleep and wait to receive a report.
Imagine the movie Groundhogs day but it never ends.
So Celestia probably has a lot of idle time to kill which has to spent in the castle because the common ponies tend to stress and panic whenever she is around. I imagine she slides around on the floor like Sweetie Belle did in was it Sister hooves social? This would be especially funny given her huge legs.
Sights like this also explain why Rainbow Dash is unable to rustle the jimmies of any of the guards. Oh the things they must have seen.