Happened with me once too. I had to give presentation in my university, in front of all my classmates and few teachers. I thought I would messed up this time and all people there will get to know that I stutter. But it was completely opposite. When I started presentation, my mouth starts to speak automatically. I didn't notice my stuttering all. I felt very comfortable there, surprisingly. I spoke non-stop for almost 10 minutes in front of everybody. I don't know how I did it. Later when I went to my friends and they start talking to me, I was again having stutter haha.