I came back from a 3 day Vipassana course yesterday. During the first day we practiced respiratory meditation only, observing the ingoing and outgoing breath, allowing our minds to become highly focused. Nothing else.
As I practiced this, my breath become more refined and subtle. While I was doing this, I had a couple of anxious thoughts about stammering. I noticed how my breath actually changed at this point. It almost stopped.
So I tried an experiment.
I continued to practice the respiratory meditation and as my breathing become more and more subtle, I watched out for anxious thoughts about stammering to arise and noticed by breathing change once again. As it did, I then breathed normally and like magic, the fearful thoughts dissolved away.