Hey, I feel the exact same way about stammering. This is the answer (imo) as to why we stammer, I recently bought a watch that tracks my heart rate, and whenever I am stammering my heart rate shoots up. But when I can talk fluently to my self or at home my heart rate is low like 50/60 but when I am out it shoots up to 90-110 and I cannot talk at all. I think there is both neurological and physiological factors, anxiety > increased heart rate > faster breathing > cannot breath when speaking > even faster heart rate and panic relax. Its a vicious cycle.