I actually posted this as a reply to someones thread, but I figured I'd post it here for anyone else who needs help with hyperventilation syndrome.
I had hyperventilation syndrome (also known as HVS and CHVS) for three years and I know exactly what can help! I actually developed a system after researching hyperventilation syndrome and going through the techniques I found on the internet.
It takes a little while, three weeks or so, but this is what I did to stop my case of hyperventilation syndrome.
Lie down comfortably, close your eyes and make sure you have a ticking clock near you where you can clearly hear it ticking. If you're a musician (like me), you probably have a metronome that you can set to 60bpm.
Week 1: Every day, for fifteen minutes, breathe in slowly - not necessarily deeply, but slowly - for four seconds and let it out slowly for seven seconds.
Week 2: Same thing, but this time, move it up to breathing in slowly for six seconds and breathing out slowly for eight seconds.
Week 3: Move it up to breathing in slowly for seven seconds and breathing out slowly for eleven seconds.
A lot of the techniques you'll find to help get over hyperventilation syndrome will tell you to start off immediately on step three, but you're already so used to breathing deeply and quickly, so for a lot of people, breathing in for seven seconds and out for eleven seconds just isn't something that can easily be done.
At first, you ARE going to feel like you aren't breathing enough. I can't stress this hard enough - YOU ARE. Your breath might feel a bit jittery and shaky while you're doing this, but that's because your anxiety has trained you and your brain into thinking that you're not getting enough air.
There will probably be times when you start feeling like you need to take deep breaths again. When that happens, just force yourself to stop what you're doing (if you can afford to) and do the 4 second to 7 seconds in and out slowly. Keep it up for a few minutes if you can.
I KNOW YOU CAN DO THIS! I battled with hyperventilation syndrome for three years before I developed this system and I've been able to breathe easily for over a year now.