This stuff can really bring about powerful alternate states of mind, and I've personally experienced some deep spiritual and psychological release from oxygen breathing exercises.
At this point I've come to think that peoples' natural response during an anxiety attack, which is to hyperventilate, might actually be a healthy, desireable reaction. But we socially repress and stigmatize it. Fear and anxiety are uncomfortable to us, so instead of holding space for working through that stuff naturally, we stuff it.
I'm telling you though, the feeling relief that controlled hyperventilating can bring is unbelievable.