What you say about the slow breathing of Kriya meditation and it's effects on cortisol levels makes sense to me. I studied Ki breathing at an Aikido dojo. The breathing is very slow, about 22 seconds as I recall for in and out breath. The breathing is done using the sound, "aaaaahhhhhh", and there are some postural considerations in the technique. There is something about breathing slowly with that sound that is very soothing and anxiety depleting. It's like a series of long sighs.The sensei (instructor) was also my physician and he had encouraged me to stuudy this as a way of minimizing anxiety. It feels very different to me than just meditiating which can be wonderful in it's own way. So if any of you are interested in using breathing to minimze stress and can't find Kriya Yoga, you might check out a local Aikido group for Ki classes. Ki classes are different that the martial art of Aikido and have more to do with centering oneself.