Many scientists, among which neuroscientist Andrew Huberman, use and teach the physiological sigh to reduce anxiety to anyone who is willing to listen.

Everything Andrew Huberman can be found here:
https://hubermanlab.com/

It is a brilliant technique that can give alleviation for anxiety and stress within seconds. No complicated exercises, no visualization, no thought processes involved at all.

It is an easy tool to teach to others, and therefore is ideal for coaches or NLP Practitioners to teach their clients.

Learn NLP?
http://www.globalnlptraining.com

A physiological sigh is a little bit different from normal sighing or breathing.. In this video the physiological sigh is explained.