I think for me silence is a part of the fight or flight response. When I dont feel comfortable where I am, I am silent. It's the flight part of the response, only I cant truly flee or remove myself from the situation at hand, but I can figuratively by being quiet. Silence in essence, makes me disappear, it lets me go unnoticed. If I go unnoticed then I cant bother anyone. If no one is bothered by me then they cant reject me. So silence is my defense mechanism.