The physiological sigh... You simply do a big inhale through your nose; try and maximize the inflation of your lungs. And then before you exhale, sneak in another brief inhalation, even if it's just a tiny micro inhalation, to maximally inflate the lungs... And then you're going to do a long extended exhale through the mouth. And typically just one, although sometimes it requires two or three, but just one physiological sigh is effective in bringing down one's level of stress significantly enough that you don't need to do it again.