Greetings all, I can say that these vertical currents are a reality as I've been in two of them. Years ago, diving with Dive Paradise on one of their EPD dives. Not sure what wall, maybe Santa Rosa, I was pushed down to a depth I'd rather not say in about a minute. It caught me by surprise and my reaction was measured. I was very easy about adding air to my bc and I eventually bottomed out. Venting air on the way back up, stablizing at a proper depth. For years I wasn't sure what had happened until I read about these events on this board.
The second time was last Feb, further down south, past Palancar. I and the rest of our group didn't get pushed down but rather could not swim upwards. I noticed something weird when the water was full of bubbles. bubbles that never rose. we were surrounded in a bath of bubbles. I eyed my depth, kept kicking up, no change. I guess if we hadn't been kicking up we might have been pushed down. We were in this zone for at least 5 min. the group eventually was able to rise, in a controlled ascent, to safety stop zone to end the dive. One of our group was a x-divemaster from Coz and she said she had never seen anything like it.
In any case, be cautious in some of the sites as they can be full of surprises.
Good Dives, SeaFlea.