I always considered breathing techniques a bit of hype, but I went snorkelling the other day and panicked. It was only after I forced myself to breathe at regular intervals rather than gasping into the mouthpiece that I began to calm down. So yes, it really did help in that situation. It's not something I feel the need to look into though, because I woud rarely have panic attacks before, and none nowdays in the agoraphobia department.