Have you ever heard Frank Girjalva explain how to regain calm in the middle of crisis or after experiencing secondary trauma?  His bold claim that we can all combat stress in under 60 seconds may at first seem unbelievable.  He shares how "stepping back", breathing, clenching, releasing, and sipping water can create a physical and mental transformation that improves our ability to think and act.  However, his explanation is grounded in science.  

Here is a great article explaining some of the science behind deep breathing, borrowing from the yogic tradition:  

Breath, Body, and Mind: The Physiology of Pranayama