Jumping in a bit late but I've just registered and I've found this interesting thread.Yeah because i also happen to have a friend who....ok it's me!
Something like that happened to me about ten years ago.I've always been accustomed to dive deep on air,I still do it.I went down to 70m. last saturday.Now I use a 12l.twinset(sorry I reason in terms of litres,meters etc. you make the calculation
),but at that time I used a single 18l..Never been badly narced but that day I was leading the dive,not because i'm a dive leader or something just because I was the most experienced diver and I happened to know the site,and in less than 40m. i suddenly felt terrible!I could hear my own heartbeat in my head,it was hard to breath and I felt like pressure on my chest,impeding sense of doom,it felt like I was about to loose consciousness. I was scared ****less...but I managed to complete the dive,fighting the urge to zoom up to surface.Thing is that even ascending to a shallower depth didn't do me any good.I remember that at the 5m. deco stop I was trying to press the valve to inflate my drysuit.The only thing is that I was in a wetsuit!
I surfaced shaken,nobody seemed to notice though.Of course I didn't say anything to anyone.Something like that can throw you into a vicious circle:you feel anxiety building up at every dive.Even at 20m. I was afraid to have another attack.Funny thing is that whenever I went on "holiday diving"that is when I was diving with a dive center with someone else guiding I was perfectly fine.It took a couple of years to return to my "former self".In those two years I wouldn't venture deeper than 25m. and I was nervous.I could only be calm when diving with a dive center!Then little by little I regained my confidence and everything has been back to normal ever since.Now I've been into technical for a few years.When I feel narced well,I just feel just a bit light headed,most of the times not even that.
I think that my episode was actually a case of C02 retention,due probably to a bad breathing pattern caused by a "hard"reg. and certainly by the psycological pressure of being always the one who led the dives.
I don't think this has anything to do with age(I was ten years younger and super fit).
Just my experience.
Regards
J.