Just say it out loud. How many times have you said it quietly, inside your head, mulled it over, perhaps even obsessed about it? Had lengthy dialogues about it in your mind, maybe even arguments. Defended your truth against potential attacks. Felt your heart beat go up, got yourself all agitated and upset when all it was was a possible conversation that took place in silence.
Speak your truth out loud. Speak it even if your voice shakes. Speak it until your voice no longer shakes. But please, speak it out loud. Get it OUT. Start breaking the pattern of shutting yourself up, for whatever reason you are doing that. You don't break that pattern by analyzing why you're shutting yourself up. You break it by noticing that you're doing it, and then doing something different. So speak. SPEAK!