I'm sure I make odd faces without realizing it, but not on purpose and not in the mirror.
I tend to have bits and pieces of dialogue from movies/TV (and lines from songs) in my head all the time, for a number of reasons--they're funny, personally meaningful or just "there" for no specific reason.
I do sometimes talk to myself, and this "dialogue" can become incorporated into it at times. I wouldn't say I get an "emotional high," but these "conversations" have helped me solve problems.
I'm not sure if this is what you meant, but that's what I experience.
Even if these situations are at all similar, I can't give you a real "reason" because I don't really know why I do it, either.
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The existence of the leader who is wise
is barely known to those he leads.
He acts without unnecessary speech,
so that the people say,
'It happened of its own accord.' -Tao Te Ching, Verse 17