I’ve decided that I’m probably not actually losing my mind. It was a result of thinking too much about what to write here and not doing enough other activities. I am now happily distracted from my problems and everything is OK.
I have seen the mouse that has been entering my apartment and keeping me awake while causing strangely little physical damage. It is not invisible; just very small. I have named it Sturbwin, which is a stupid name that I will never use for anything else.