I act the same way!It's funny. When I daydream sometimes I forget I have SA. I get really carried away with it. When I'm thinking about somethign particularly intriguing I physically get riled up. Sometimes, I don't know if I'm only moving inside my head or if my limbs are actually swinging around.
ALSO, I sometimes mouth my daydreams without realizing it. Like, mouth what I'm saying in my daydream.
But I agree, I don't think day dreaming causes it. It only exacerbates the anxiety because you live in a fake world.