There's been a few threads about downwellings in the Incidents & Accidents section of the forum. One of the theories of safely getting out of one was to inflate your BCD to try to prevent from getting pushed down further. However, that was countered with the argument that an inflated BCD gives more surface area for the current to push down on. Also, when you're out of the downcurrent (or when it stops), you're now at depth with a fully inflated BCD - not good.
The idea that seemed to make the most sense to me was to swim horizontally. I liken this to being under the stream of a waterfall. What's the best way to escape from the water pushing down on you? Swim across the water - don't try to fight it by swimming up.
There's also the possibility of safely clinging to the reef until the downcurrent is over. Some of the reef can cut you up real bad though. However, in Cozumel you're not allowed to use gloves in the marine park
Even then, there's no telling how long the downcurrent will last. I think this would be the most instinctive maneuver for anyone suddenly descending beyond their control.
You can probably find some threads on the subject by searching for "downcurrent", "down current", "downwelling", "down welling", "downdraft", or "down draft".
I'd also like to point out that these things can happen anywhere on the island, even at the "regular" sites along the west side. I know someone who was climbing onto the back of a boat while it started spinning (clockwise?), which is a sign of one. Thankfully they were getting back on the boat because the dive was ending. Talk about good timing.
Has anyone ever been on a dive to the north dive sites, Canterall, Barracuda etc and ever been taken by a downwelling or upwelling? How did you escape it? Did you get hurt at all? 
