I took me a long time to admit there was a problem on this dive, much less that it might be an "incident".

I was testing a prototype rebreather, with a new buddy. He told me from the beginning about where he usually turned this particular dive, which was fine for the test I had in mind.

We were going up the mainline in Devil's Eye. The vis was pretty bad, and the current was high. At about 1000' in, my buddy flashed me. I knew he was about at turnaround, so instead of responding, I started a slow turn around, taking us off the line. He followed, continuing to flash me. I remember thinking "why is he still flashing, doesn't he realize I am turning?" So I acknowledged his signal, and indicated that we exit.

I suddenly realized that I was off the line, and couldn't see it in the low vis. I found it in a few seconds, and started following it. It took me a few more seconds to realize there was something not right. At the time I couldn't figure out what was wrong. Thinking back, I didn't see my buddy, and I was still swimming hard. I was trying to catch him, I guess, until I passed an arrow. I remember thinking it seemed strange, but I had gone a ways past it before it hit me. It was pointed the wrong way. Now I know it was ME having the problem. I felt like I was in slow motion. I looked at the PPO2 gauge, to see if I was getting hypoxic, but it was fine (about 1.2). I started to wonder if the rebreather was malfunctioning. I had taught myself that if I ever suspected a rebreather problem to bailout to open circuit. So I switched to backgas (EAN34). In just seconds, I felt better, and realized I was still swimming upstream, and not out! I turned around, and could just barely make out my buddy in the distance. I swam fast to catch up. I am not sure he ever realized I wasn't behind him.

At this point, I decided to try out the rebreather again, it was fine now. I chalked it up to paranoia, and put it out of my mind.

After reading about several other divers with the same symptoms, I realize now, that I was suffering from CO2 excess. I didn't get any of the symptoms they warn you about, shortness of breath, headache, blue lips or nail beds, etc. I only noticed that I was slow responding, and making potentially fatal mistakes. I am sure that if I hadn't bailed out to open circuit, I would have kept swimming the wrong way until I finally blacked out.

Moral: CO2 excess is a subtle problem, and can hit an open circuit diver as well. At depths over 80' it adds to narcosis, making you unaware of any potential problems. If you feel anything is wrong, stop, and see if catching your breath helps. In any case, if you have a bad feeling on any dive, it is probably better to abort the dive.

PS. I now use a larger scrubber, to prevent the problem.