Some years ago, one of our experts, an experienced SWAT officer, asked for a drill to control and reduce stress (specifically, the kind that that arises on a dangerous mission like a hostage rescue or raid on a terrorist safehouse). He received a simple drill on rhythmic breathing and visualization. Its essence was to inhale, stop, and exhale in four-second increments for each segment, while paying special attention to the moment when the air flow changes direction. This drill should be done during the preparation period before the stress-inducing action begins, and also on a daily basis.
The next time we met, the officer told me, "This drill changed my life." It enabled him to control his mind and the stress during missions, be more focused, and function much better.
Imagine, after over 15 years in the unit, a simple breathing exercise changed his life.