That is another example that stuttering is, at some degree, psychosomatic. It goes away and may return in another occasion. In my job I don't have to talk a lot, so I can keep things stable at some point, but I suffer with the same sometimes when I have to say something to someone and I block. The anxiety and the despair have been my friend for a long time. Honestly, I don't have much to help you, but I'm reading a book about stuttering and it's helping me a lot. It calls "Suttering & Anxiety - Self Cure", by Lee Lovett. I hope that helps you too. If you wanna chat with someone about it, I'm here.