I'm hoping for a bit more on what to do when you see the 'sand tornadoes' (other than 'take pictures' as I have) - and what I think the consensus is, in regards to what to do if you find yourself in the down current, is to swim away from the wall. R (husband and dive buddy) says also to keep an eye on the soft coral on the wall, and if it is bending down avoid that area.
Again, this is all assuming that we notice something peculiar in time to remember what to do.
Also try and watch what any particles ahead of you are doing. Instead of staying pretty stationary or going horizontally across a wall, they might be heading downward or swirling.
Everything I have read says to swim away from the wall. Eventually, the "waterfall" loses it's reach.
That was my experience in Belize while cave river tubing in fast, high water right after/during mainland flooding. Just before we converged toward the wall of a particularly fast moving cave river that most sat out, the guide yelled, "kick away from the wall!" to redirect our tubes that we had daisy chained with our arms. The girl beside me pressed my tube down as she kicked off the wall and my tube flipped. I was dragged down by a downcurrent and held under at least 10 feet - WITH a lifejacket. I held my breath and kicked up with all my might, to no avail. I suddenly remembered what he had said and kicked off the wall as hard as I could, and I shot away and up in a split second, getting rushed through and spit out at the mouth of the cave.
Here in the St Lawrence river, usually only people with doubles or who have very good gas consumption are allowed to do the Lillie Long Drift by the charters. Only doubles divers who have proven themselves are allowed to do the Lillie Extra Long Drift. Both of these routes have converging currents with downcurrents, upcurrents, and back eddies, and require strict adherance to the depth and timing intervals given in the briefing.
I know a diver who got whisked down to 170 feet in seconds on the Lillie long drift and then swam out.
I have had a couple of buddies who didn't realize the importance of getting down to the first target depth (90 feet+) quickly, and got whipped up, down, and backwards in that nasty 40 - 80 foot range with me strongly signalling them to come down.
Even at 90 feet, we can still get pushed to 102 or so for a short time.
In Cozumel way back, a couple of divers on our LDS trip on another boat went from 90 feet to 130 feet, and then got spit out. After filling their BCD's, it took time to deflate and slow their rapid ascent. The instructor initially said that the other 2 divers must have lost control of their buoyancy simultaneously, but it later came out that he swam his way out.
From my and others experience and from reading, getting away from the wall seems to work, as you said. It seems that going across the downcurrent in any direction (away/toward the wall) or across the wall may work. I'm not confident in swimming toward the wall because that's where the current is rushing down and converging with the cross current. Trying to swim up or inflating a BCD, SMB or lift bag is likely futile. Once you get out of the downcurrent, you have a runaway ascent to deal with too.
scubaboard.com
It's a little faded but not much. It doesn't get out much. I do test it every trip. 
