Well, I've never been much for those breathing excersizes. I have to get to another, empty room usually. What I do is think of something a pyschologist taught us once. It goes:

"Think of ur favorite place in the whole world. Visualize it as clearly as u can; after u got that, walk thru a door and into a big house. In this house there is a staircase with ten stairs. Walk up the stairs, and each time you take a step, inhale deeply. Once up the stairs u see a room. You put ur hand on the door handle, and its cold. You twist it open and walk inside. This room is all white and it only has a chair inside, that sits in the center. Sit on the chair and clear your mind. Think of nothing but the room. When you are done, go back down the stairs (inhaling with each step) and then go back out the door to ur favorite place."

Sorry its so long- cant believe I remembered that whole thing. It works if you really visualize.

Now this might sound stupid but it's the only thing that works for me. When I have a panic attack the worst part of it is the breathing. I can't catch my breath or take a full breath. This makes me panic even more. So I've learned to make myself cough. When you cough you naturally take a full breath and fill your lungs. This relaxes me a little because I know, if needed, I can breath. Now that I'm a little relaxed, I try breathing slowly taking a deep breath, filling my lungs slowly and then releasing. If I still can't do that I make my self cough again until I can.

I was told by a nurse to take a deep breath through your nose and count to 5 and let out through your mouth.. I cant say it has worked 100%, but helps calm the attack down a bit and make it not as extreme for me.