--writing to Grandpa L. as specified (this is markgritter's maternal grandfather, technically, but there's a point with each in-law where you shift from thinking of them as the other person's to thinking of them as yours -- at least ideally there is -- and with Grandpa Lyzenga and me, that took about 3.2 seconds, and he is just the very most you could ever ask a Grandpa Lyzenga to be)
--cleaning up a bit of my desk mess, which is there because I hate desk mess and will therefore deal with things put on my desk to drive me nuts
--reading a little of Blood and Iron, then stopping because getting all wrapped up in someone else's book wasn't really the point here
--drinking more water and taking an Advil
--playing with the dog
--putting on music
--putting on different music, and that finally did it -- thanks, markiv1111 (and thanks dd_b for being my supplier). Don't know why "The First Overnight Guest" did it, but there it was, "There's a chance of rain but no real chance of rest," and my brain went click click whirrrrr...and then it was behaving sensibly again.
And now I'm in late-afternoon crash and have learned not to beat myself up if I'm not useful for an hour or two, because I am definitely a morning person and sometimes an evening person, but what I am not is an afternoon person.
What are your favorite brain-reset tricks?