You’re not stammering at this moment, yet you’re becoming scared that you might.
You’re not even going to stammer tomorrow, but you are reacting to thoughts of you stammering. Unfortunately, engaging in such fantasy is like a self-fulfilling prophesy. It usually becomes true.
The only time you will stammer (in terms of the physical act of stammering and blocking) will be in the present moment. Yet you create anxiety and fear long before the actually stammering episode.
As I said the act of stammering only happens in the here and now. All the worry and feelings of anxiety and helplessness are ‘mind stuff’, which is just you reacting to internal ideas and concepts – too much thinking!