How about meditating? Works for a lot of people. Even I do it on occasion (I'm about as skeptical as they come), but there is good evidence that the biofeedback works to reduce stress. Personally, I like the one imagining I'm lying on a beach at sunrise (the sun warms my toes, legs, torso, etc.). Another good one is a walk where you visit a waterfall and put down your heavy backpack (metaphor for your worries).
Hope this helps. Failing that, there's medication I suppose.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh