In my case at least it seems like a PTSD response. When I was a little kid I used to have to rush my words because my family would never let me finish my sentence they would always talk over me, so I would rush my words get nervous & stutter. Then when I would stutter in front of other kids they would all laugh & make fun of me. So it seems like it's a deep embedded ptsd response that I still get now at 31. I still expect to get made a fool of when I stutter around people and I feel like I can't let that happen.