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Well, I usually don't lose my speech for good when really upset/frustrated, not as in "no matter how hard I try, I can't get a word out". I just get some sort of "language hiccup", so at one or two words I start to stutter until I "hang up" at some word (repeating it twice, thrice or more until giving up) for good. When I try to rephrase what I tried to say before, it can happen quite often that I just forgot it by that time and then I'm so to say "speechless". This is sort of ironic, considering how that "language hiccup" as I like to call it, causes further frustration, which worsens the situation. Though it's definitely not funny when it's happening.
It can be embarrassing, to be honest, but luckily I don't get upset or frustrated to such an extreme extent that often, I have a fair amount of self-control and usually try to remain calm.
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Diagnosed with Aspergers.
BSP-errors are awesome.