I do this a lot too. I remember in the 9th grade, when I learned how to type without looking, I typed every single word out in my head (and it was getting annoying after awhile). Then I started playing this mind game where I had to figure out words that had equal amounts of letters that I typed on each hand to where it balanced out (like 3 letters on the right hand, and three letters on the left and what not). I also have practise conversations, but I don't very often type them in my head; it doesn't mean I don't, however. Lots of the time when I'm alone or I'm out running or I'm just plain lonely I have conversations by myself with someone I want to talk with (I know they aren't really there, however; that'd just be weird to imagine your friends there in your room, and then they just came out of nowhere lol. I'd be scared! lol)
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I'm 24 years old and live in WA State. I was diagnosed with Asperger's at 9. I received a BS in Psychology in 2011 and I intend to help people with Autistic Spectrum Disorders, either through research, application, or both. On the ?Pursuit of Aspieness?.