[SketchySeaBeast]

That first one feels very chicken and egg - if you're anxious your sympathetic nervous system is going without the breathing. Can breath be used to relax you? Absolutely, but that's as much about focusing the brain on the breathing instead of the anxious thoughts as anything else.

[jerf]

It's a reasonably well established principle of psychology (real science, not pop-sci) that a surprising amount of what you perceive to be your emotional state is mediated through your body. That is, you experience a stressor, so the "low level" portions of your brain activate bodily reactions to that stress, and what your high-level brain perceives as stress is actually the bodily reaction rather than the original stressor. Exerting such control as you can on your body (since it is non-zero, but not total either) is a legitimate way to control your (perceived) emotional state, which then feeds back into the entire system.

(This also factors in to how hard it is for some people to figure out why they are stressed; the part of the brain trying to work that out isn't necessarily as connected to the stressor as you might intuitively think.)

I've been having some low-level morning sleep paralysis lately (it has come and gone my entire life, & it has never been remotely as bad as I've heard some people describe); recently I've discovered an easy way out of it is to just hold my breath (or really, just stop inhaling), which triggers just enough stress to break through the paralysis. YMMV.

[rrrrrrrrrrrryan]

I had sleep paralysis as a child once in a while (which isn't uncommon), but as an adult I only get it after a period where when I've consumed cannabis with some regularity, then stopped.

It may or may not apply to you, but my friends that have sleep paralysis say this anecdote holds true for them as well.

[monadgonad]

Similarly, I get it if I've been drinking a few days in a row, then stop. Both of these drugs suppress REM sleep so my theory is that the sleep paralysis is a rebound effect.

[ycombinete]

I went snorkelling for the first time, in Mauritius. Flat water, no fear to speak of. But I was breathing incorrectly through the snorkel. Which one does the first time they snorkel. Overly deep, heavy breaths. Suddenly my heart was racing, and I went into a panic. It felt like I couldn’t breath at all. I started hyperventilating, breathed in some water, and started to get tetany which of course made everything worse.

This was all brought on by my breathing wrong. Not out of stress. Simply because the snorkel messed with my normal rhythm, and caused accidental hyperventilation.

[james_s_tayler]

Breathing is directly connected to the autonomic nervous system. Inhaling activates your sympathetic nervous system speeding up your heart rate and increasing the amount of electrodermal activity in your skin. Exhaling activates the parasympathetic nervous system slowing down your heart rate and decreasing the amount of electrodermal activity in your skin.

You can measure it with HRV and skin conductance sensors.

[betenoire]

Anxiety is irrational. addressing your physical symptoms in the moment is FAR superior to being introspective. Save that for your personal retrospective after the anxiety subsides.