I can completely sympathize with this thread. I recently had similar experience that took me COMPLETELY by surprise. I went to a Scuba summer camp on Catalina Island when I was a teenager for a couple of years. Being a 3-week summer camp with 8 or so dives a week, we had time on our hands so our training was SUPER thorough and after basic certification all the dives we did just kept building on our skills - there was no such thing as a "recreational" dive. I logged 40 or 50 dives including all sorts of specialties - night diving, deep diving, wreck diving, navigation, photography, etc. etc. etc. By the time I was 16 I was a pretty experienced diver with a ton of training. If anyone reading this has kids you should check this out. It was an amazing experience and incredibly educational - surface intervals are filled with courses on marine biology, conservation, sailing, etc. It's been 25 years or so since I was there but the pictures and descriptions on their website make it sound pretty much exactly the same today as then.
Catalina Sea Camp - Marine Biology and Island Adventure Camp for Teens.
When I was 14 on my first dive (there was no pool - they just pushed us off the side of the dock!) after that first having to force myself to take a breath underwater I took to it like the proverbial fish to water. I had no problems at all and was COMPLETELY comfortable underwater. I thought it was the best feeling I had ever experienced. I LOVED it.
Fast forward a couple of decades of no diving and I have a son who is 12 and an upcoming trip with Scuba opportunities and it's time for him to get certified. I'd long since misplaced my PADI card and dive log (I'm certain they're buried somewhere in my Mom's house) and obviously extremely rusty so I took the course with him.
I remembered most of it and skills like buoyancy and mask clearing were no problem whatsoever. But I hadn't counted on an anxiety issue - especially around my breathing - that had snuck up on me. The signs were there - I get weirded out when concentrating on my breathing for Yoga and I had to bail out of an MRI tube due to claustrophobia last fall - but hey, Scuba's one of the highlights of my life and one of the greatest feelings in the world, right? Well, I kneeled down in 4.5 feet of water and lasted about a minute before I had to bail out, extremely shaken. No mask clearing or anything else. Just felt smothered. We had three nights of pool work and I had to skip the first completely. After I expected it I was able to get myself together on subsequent nights but still a bit of a struggle.
I'm working with a doctor now on my anxiety issue - it's more generalized than just Scuba and I'm not going to let it keep me from the things I love. I can do it now but I'm still not 100% comfortable or relaxed. I really enjoyed our open-water check-out dives this last weekend at Blue Hole in New Mexico and we did a couple of dives on our own after the checkout dives. I really had fun but it was still very stressful. I was sloppy in my technique due to the distraction of worrying about my breathing and sucked down air at a prodigious rate!
I can offer two tips:
1) Distractions. This is key for me. In certification classes I had the most struggle while I was sitting there waiting for the instructor to work with other students. I look at my gauges, play with my buoyancy, try to fix a wrinkle in my suit, anything. We brought a GoPro to blue hole so I'd mess with it's settings while waiting around.
2) Bach Rescue Remedy available at any health-food store (Sprouts, Vitamin Cottage, Whole Wallet, etc.) does wonders for minor anxiety with absolutely zero side-effects. Obviously try it on yourself before you take it diving, but it's a homeopathic remedy I've never known anyone to have any sort of adverse reaction. Most people do report that it takes the edge off. Don't expect too much it's not like taking a Xanax or anything (which is why I think it's safe for diving). Just a little help.
Chris