Slow breathing is also recommended for novices before public speaking, as it helps speakers overcome irrational physiological fear of facing people, the risk-taking shift is useful as it helps you speak more confidently, not more cautiously. Slow breathing can calm nerves quickly; bottom-up regulation: body tells brain “you’re safe”.
Slow breathing (in yoga: pranayama) instantly down-regulates your nervous system by boosting vagal tone and lowering sympathetic "fight-or-flight" activity. When your breath lengthens, it signals your brain that you are completely safe, dropping your heart rate and lowering blood pressure.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12858147/