Dr. Lecter, I am not a tech diver, but I think I see the point that several posters have made regarding your initial choice of gas being part of the issue here. I am not coming at it from the standpoint of saying that it was the wrong choice or right choice to pick that mix for the dive. Instead, I am thinking that YOU likely felt some level of concern with the ppO2 of your gas choices that led you to respond the way you did to what was probably a thimble jelly sting based on your description of what you saw in the water.
If you can stand a little story telling, I think I can maybe explain what I mean. Many years ago, my wife and I were renting a house down the street from a guy who was habitually drunk and who apparently liked to beat his wife. His wife called the police on him one late afternoon and with all the lights and commotion outside, my wife and one of the neighbors happened to be standing out on the sidewalk watching as the cops walked the guy out of the house in cuffs and stuck him in the squad car. As the cops drove away, he was staring out the window of the car at my wife and the neighbor with a scowl on his face. My first thought at that moment was "great...when he gets out and comes home, next time he gets drunk, he is going to have something to be upset and irrational about instead of his wife".
I didn't think much about that for the rest of the evening. Around midnight, I was sitting on the couch watching latenight tv and heard a tremendous crash in the kitchen, and the immediate image that popped into my head was that it was the drunk from down the street, out of jail and trying to come into the house through the kitchen window. I jumped up and ran to the bedroom to get a gun, while yelling at my wife to call 911. When I went back around the corner from the bedroom, I could see into the kitchen and saw that the source of the noise was a potted plant that our cat had been chewing on and had pulled off the windowsill and into the sink on top of some plates and glasses. I managed to slow my heart rate down and stopped my wife before she actually got 911 dialed. I am not sure who was breathing harder, my wife, the cat, or me...but we can all laugh about it now looking back.
The reason I recount that story here is this...the immediate leap of my mind to think that the sound came from the guy coming through the window was completely irrational for several dozen reasons. The window there was small and high off the ground, and would not be the window of choice for anybody trying to break into the back side of the house. There is no way that guy got out of jail that quick, and there is very little reason why he would have tried to come into the house that way if he had. I could go on and on...but the point is that because of a little pre-thinking about a future hazard, my mind when it panicked, skipped past several rational explanations for the sound I heard (cat being high on that list) and immediately settled on an irrational explanation instead. I reacted based on that irrational perception and went from there.
In your case, you mentioned having seen a number of jellyfish in the water during the dive. In most cases, if you felt a tingling/stinging sensation during a dive when you had been seeing jellyfish, you would immediately think "marine sting"...not Ox Tox. I believe it was only that you had selected a gas mix that put you beyond the widely recommended ppO2 for your dive that caused your mind to immediately assume Ox Tox when you felt the sting. As a result, you considered ommitting planned deco and deviated from your dive plan. I am not trying to say that those actions were right or wrong, or prudent or not. But I think even if you won't admit it to yourself, your subconscious mind knew that you were doing something dangerous by choosing to dive that gas mix, and in the moment of decision, it caused you to skip the obvious marine sting possibility and jump to the conclusion that you might be suffering from Ox Tox instead. If you had assumed marine sting underwater, but then considered the OxTox and deviated your plan accordingly, I could see it being a rational series of events. But to skip past the obvious explanation to one that was much less likely (albeit signficantly more dangerous) suggests to me that your initial choices on the dive altered the way you reacted to an unexpected event. It turned out ok for you in the end, but I think it is wrong to dismiss the role of the initial gas selection in affecting how you reacted later on down the road.
