Matt, I looked at your tracklog. The point at which you were sinking rapidly shows that it occurred in front of the ridgeline. It also shows that your direction of travel was NE, back towards the ridgeline, rather than SW, moving away from the ridgeline. Your tracklog shows that your direction of travel was the same as your drift in the first thermal.
So if we assume that you were headed SW, it seems that you were actually going backwards in sink.
You might have been in between two large parts of the thermal. One sucking you down and backwards as it pulled you from behind. The other was in front of you, waiting to screw around with your wing.
In any case, Those aren’t places I’d want to be in a paraglider.
Paul Murdoch