While it's easy for some to dismiss "mystical" aspects, look at the real world applications. If you suffer from "pressure" that could be a moderate form of anxiety. A great combat to the parasympathetic response? Breathing.
Watch what happens when you get punched in the gut. Your immediate, initially uncontrollable desire is to blindly fight like hell or turn and run. Keeping a calm head takes practice to overcome the rush of hormones. Breathing slows the heart and tempers the response. It's the same reason elite athletes, especially runners, know the power of proper breathing.
I tend to think many mystical aspects had some physiological root that then got adulterated over time. Breathing as the route to relaxation is first on my list.