[Zelphyr]

Simply breathing through a straw may not do it. My therapist had me run up and down a flight of stairs for about 30 seconds and then breathe through a straw cut down to about 3 inches while holding my nostrils closed.

Your body thinks you're not getting enough oxygen. You're getting plenty, it's just that it all coming through that tiny hole tricks your body and that triggers panic sensations. Doing that several times exposes you to those sensations and you eventually get used to it and allows you to manage more intense sensations.

[moldavi]

I'm not sure that's correct. I've heard that high CO2 levels trigger the parasympathetic nervous system which calms us down. One could get the same effect from breathing into a paper bag, I think.

[hanche]

Hmm. In the Apollo 13 movie, high CO2 levels triggered a panic/anxiety attack in one of the astronauts. (Which may not have happened, or not as severely, in reality – but that’s adifferent issue. For one, astronauts are trained not to panic.) A quick google seems to confirm this. As for breathing in a paper bag, I believe that is one common way to deal with hyperventilation, which may also induce anxiety and thus lead to more of the same.