I really feel what you’re describing. I used to feel physically sick before presentations. I’d stay up late practicing again and again, just to make sure I didn’t stutter even one word. But the next morning, I’d feel exhausted and then block so much that I could barely say anything. I remember feeling so embarrassed. I blamed myself for not being able to speak even a single word. What really changed things for me was accepting my stuttering and allowing myself to stutter. Since then, I don’t blame myself anymore when I block. What also helped me is scheduling small speaking tasks and completing them regularly. That gave me confidence, little by little. Before, I was so anxious when someone tried to talk to me, my brain just shut down, I couldn’t even concentrate on their words. Now I can react more peacefully. Not perfectly, but with much less fear.