I came across this breathing technique through one of my teachers. It is really easy and really powerful. Breathe in for 3 seconds. Hold for 3 seconds. Breathe out for 3 seconds. Pause for 3 seconds and repeat. After 10 minutes your physiology calms down as it matches the rhythm of the 3,3,3,3 breath.
Elite soldiers and sports people use it under heavy pressure. I use this as a way to relax my body before sleep, or in tense situations. When done for 10 minutes or longer, it is impossible to feel any negative emotion. Give it a try.
I've created a list of all the things I've done over the last 15 years that have reduced anxiety for myself and for the people I have worked with. I'll share one a day for the next 37 days.
https://inspirehypnotherapy.com/37-proven-ways-to-reduce-your-anxiety