My darling ladies dancing/lords a-leaping: please someone explain how my clothes are defying physics and gravity today!

I’m wearing a pretty knit dress with tights and boots, an outfit I’ve worn dozens and dozens of times.  And as things often do in such ensembles, various items of clothing are doing a bit of shifting.  Normally this is manageable, but please.  Please explain why suddenly my tights are struggling to stay up while my slip has maneuvered its way up to my rib cage.  Twice.  It’s a miracle I haven’t endangered my job or offended some little old lady beyond repair with a major wardrobe malfunction!