Mine is probably pretty similar that the one that Dr Weil has recommended:

(1) Sit in a chair, feet, no shoes, flat on the floor (grounding!).

(2) Fingers from both hands on your stomach around your navel, just touching.

(3) Breathe in deeply so your stomach expands and your fingers move apart.

(4) Count to five.

(5) Breathe out so your stomach collapses and your fingers touch again.

(6) Count to five.

(7) Repeat (2) to (6) for about 15 minutes.

I don't know how good the evidence is but I have heard that panic attacks can be triggered by shallow breathing, leading to abnormally high blood CO2 levels. I am unsure about the physiology but this one works for me.