Please don't feel stupid or delete the post. It's a very good post and an excellent question and I am sure many can relate. I would think the flailing is a stim since to me it sounds like you may be overstimulated and your body needs to release that. When I am overwhelmed, overstimulated or sometimes exhausted, I get like you were where I don't have the mental capacity to figure anything out. Usually a good rest in a quiet dark place helps me tremendously when I am like that. Sometimes a good meltdown helps too. Keep us posted on how your assessment goes and whether you are on the Spectrum.
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"I'm bad and that's good. I'll never be good and that's not bad. There's no one I'd rather be than me."
Wreck It Ralph