I have done this since I was very young...is it an ASD thing? I thought everyone talks to themselves...though I suppose it all depends on how much one talks to oneself.
My problem is that I don't just do it when alone, I often talk out loud when I am out in public, especially if something or someone has annoyed me, and then people look at me. Sometimes, I actually wake up and as soon as I am awake, I find I am talking to myself almost manically, lol.
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I am diagnosed as a human being.