I usually talk a lot. I try to get a lot in all at once. Only later does it occur to me that I should stop to see if my first point is getting across before I move on to the next five.
There have been a few occasions when I did not talk. The only one I can clearly remember is shortly after I got beat up by thirteen older boys in the gym locker room, locked in a locker and then pounded again when I got out. Almost twenty years later, it occurred to me that I was in shock when, about a week later, I was deliberately defying some more older boys by refusing to speak. I was standing over a campfire of all things and these guys were demanding I talk. I remember thinking that I was asking them to beat me up again. One of them tackled me. I just got up and shook it off and didn't really analyze for about 20 years.
I'm not sure if this is the type of selective mutism you're talking about, but your post stimulated this memory. I think I'm still learning about this kind of thing. I only found out I'm an Aspie earlier this year (at age 34).
thanks
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"Nothing becomes funny by being labeled so." -Strunk & White's "Elements of Style"