I usually dive the first dive of the day in Cozumel on air, due to the fact that they are deeper dives on walls with the "potential" for down-currents over depths that could exceed Maximum Operating Depth for 32% or 36%. All other dives during the day are on 36%. I dive Nitrox for the added safety factor and I do a lot of dives on dive trips. I have experienced a significant downwelling only once in Cozumel, but it was significant and it was just recently (this past December). We came through a swim-through at Palancar Deep and out on to the wall at 90 feet. Next thing I know, the bubbles I was exhaling from my reg were not ascending- they were staying in front of my mask, clouding my vision and I was descending pretty quickly. I was prepared for such a potential occurrence, but my wife wasn't. She panicked and put the Darth Vader death grip on my right bicep. We were both descending and as much as I would have preferred to swim out and away from the wall and out of the down current, it was obvious that I wasn't going to be able to get my wife to go along with that - even though we had discussed the possibility of downwellings and what to do in the past. Only option in the moment was to try and inflate and hope that I could pull the both of us up and out of it. I only had my left hand to work with due to her grip on my right arm. We got up and out of it, mostly due to the fact that we were both very perfectly weighted and not overweighted, as so many divers are. Back on the boat, I checked my computer to see how far down we got pulled-- it read 130 feet.