This issue was brought up in another thread but I think it needs to be posted here as well.
Also from that thread:
(edited) Shallow hyperventilation is sort of like panting. When someone starts to get nervous (even if they don't realize it) or maybe starts working harder than planned, it can be a common breathing pattern.
The problem with shallow hyperventilation is that you are now not exhaling fully. So what's happening is that the CO2 your body is producing, which would normally have been expelled when you exhale, is slowly building up.
As you were (hopefully) taught in your basic class physics discussion, CO2 is the stimulus to breathe. The more CO2 we have, the more urgent that need feels like.
When you shallow hyperventilate and the CO2 builds up, you start to feel like you can't catch your breath. You may take a breath off the reg and it doesn't satisfy the feeling of air starvation. But it has nothing to do with you not getting enough air IN. It has to do with you not getting enough CO2 OUT.
So if you find yourself in this situation, the thing to do is . . . EXHALE. As big as your can. Take a breath. Exhale BIG again. Take a breath. Exhale BIG again. Generally two, three, or four BIG exhales will blow off enough CO2 that the not-getting-enough-air feeling will go away.
And once you get rid of that need-more-air feeling, you can decide whether or not to continue the dive. To me, this is all part of the walk-away lesson from your experience. Thanks for sharing.
- Ken
Also from that thread:
Ken - Sounds similar to what happened to me the first time I was 85 ft. I started experiencing tunnel vision and felt my reg was not giving me enough air. I looked at the other divers around me to see if they looked the same as how I felt, they did not. I looked at my SPG which told me I had more than enough air so I took deep inhales and exhales until the tunnel vision went away. I felt comfortable enough to continue the dive after the tunnel vision went away. My first and last time I ever had that experience.
FWIW, there's research to suggest that CO2 retention exacerbates the effects of narcosis. At the very least, it interferes with adequate oxygenation of...the brain. Ken's recommended technique to slowly inhale and exhale fully can effectively head off these problems before they become a real issue. This is definitely something that should be taught to students before the deep dive of the AOW specialty.