just play relaxed, regardless of what you're playing. playing relaxed shall dictate how you breath. and it's easy to do; enjoy the music and listen to your bandmates. the only problem with this is when you encounter a crappy PA system where you can't hear anything properly, though this can be circumvented by rehearsing enough. heh.
i somehow learned how to play relaxed maybe because of watching billy ward's dvd, "big time" (huge inspiration. watch it and he'll instantly become one of your favorite drummers.). i also learned how to keep track of time using breathing and other mechanics-- i breathe in deeply during "1", and my breathing is constant throughout the song (i think).
back when i didn't breathe properly, i panic then speed up. it doesn't happen now. during our first gig, i panicked because of the equipment. that lead to me making bad choices on fills-- fills which could've been way better-- but i never sped up. yun siguro ang importante, having a steady pulse even during a bad day.
whew. sorry. long reply.