I know exactly what you mean. I had just joined college and I was giving the first presentation of my life. I had been stressing over it for weeks and I was 100% sure that I would embarrass myself in front of class. When the moment came, I went up ahead and just said to myself, "Okay here it goes.." and started giving my presentation. To my surprise, I didn't stutter even once. In my mind, I would be like, "Any minute now..". But nope, I didn't even stumble on any word. I was so surprised and excited that about the time I reached the middle of my presentation, I had completely forgotten about my stutter and was speaking passionately about the topic. The presentation went great and I was among the two best speakers in class. My classmates were surprised because they had never heard me speak so openly. I thought to myself, "Holy shit. My stutter is cured." But then I tried talking to one of my friends and nope it was still there. Haha. But anyway, now I don't freak out about giving public speeches as much as I used to.