With regular practice, you create a well of calm to dip into as the need arises.
One way is to invoke the "relaxation response," through a technique first developed in the 1970s at Harvard Medical School by cardiologist Dr. Herbert Benson, editor of the Harvard Medical School Special Health Report Stress Management: Approaches for preventing and reducing stress. The relaxation response is the opposite of the stress response. It's a state of profound rest that can be elicited in many ways. With regular practice, you create a well of calm to dip into as the need arises.