I've stuttered my whole life (M20) and I don't have physical pain. When I block it feels like I'm not breathing (cause I'm not) but it doesn't hurt. It more internal (the feeling of shame or anger after stuttering or having somebody complete my words). Going off of that I wanted to say that I often don't like people finishing my sentences in private settings (family, friends, etc.) because I feel like i have time, but am more open in public where I can just get through the situation (ordering food).