who are you, and what are you doing in my head?
but seriously, I have to same problem and I don't know what to tell you. I often imagine conversations with people, but when I get a chance to have said conversation I can't make the words come out. or I will start talking, but then cut the conversation short. it's not that I want to stop talking, I just can't make the words come out. it's frustrating to have more that I want to add and not be able to say it. and those times that I do manage to start again the person(s) I was talking to have moved on.
It's gotten so bad that I don't talk much anymore, I can't seem to get the words out in an intelligible manner, and even if I do it's not like anyone pays any attention to what I said.
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I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it.
-Terry Pratchett