same thing happened to me, but I know the triggering event. final year at college we were told we would be doing a presentation in front of the year group at the end of the year. the anxiety hit me right away, and suddenly my stutter came back, and got worse over the year. it was a group presentation and I ended up being the guy who operated the lights, and had a plant in the audience ask a question inknew the answer too so I could speak. it was awful. it continued to get worse over the next 18 months until I went on a program to help. been doing well for the last 20 years, until work asked me to present something. immediately I felt my chest tightened and found it hard to speak. thanks to the program I now have the tools to deal with the anxiety. good luck to you.