For me, the under-stimulation on the outside leads to simultaneous over-stimulation on the inside, if you know what I mean π€£ If I don't have things to do, be it movement like walking or yoga or skiing or riding or activities like games, or sensual inputs like sounds and lights and touch or communication or meditation and crystal work or watching a series or reading a book my overthinking mind will start popping up with - usually - not so nice topic offers and usually I'll then get myself upset, depressed, ashamed, etc. so I rather am a little "duracell bunny" always up and doing something except for when I plan to sleep π₯Ή
Also I'm a absolutely stimmy person, always twirling my hair, circling my feet, ...
Sorry for the long answer but to cut a long story short, that's my experience of it and how I adress it π€£π€