I think you're sort of assuming that people are hyperventilating due to anxiety - this is just one of the possible causes. Usually, if someone's hyperventilating, it means that for one reason or another, they are not getting enough oxygen. EMTs have very few diagnostic tools, and blood pressure, pulse rate, and respiration are the ones that indicate the most serious problems - someone hyperventilating is generally very close to becoming an unstable patient that needs intervention right away.... This is a bad sign that indicates pending respiratory failure, a cardiac issue, shock or allergic reaction, overdose, lots and lots of bad things. For some of these, oxygen alone will fix it, in others you may have to "bag" (provide manual respiration for) the patient, or address the underlying cause of the hyperventilation - by removing them from a toxic environment, or treating an allergic or asthmatic event. So, sometimes, Someone gets anxious - > they hyperventilate. More often, Someone hpyerventilates -> they get anxious -> they hyperventilate more -> things get serious. If someone's just hyperventialting because they're freaking out, and they're relatively sane, they generally find it almost irresistible to follow you if you sit in front of them, tell them what you're doing, and calmly, insistently, visibly, breathe slowly. It's like how you have to yawn if you see someone yawn...