We were going under an overpass when an 18-wheeler breezed past us. We felt the rear-end of the trailer shift, so DH let off the gas and applied the trailer brakes(you never hit the tow brakes!) Just before we passed out the other side the 18-wheeler gunned it and we think the draft from the truck caused some suction under that low bridge. He just did clear our car when all hell broke loose. It took just seconds, no more than 10 seconds max.
The rear started to swerve and then it really started pushing us back and forth. There was a moment when I felt the car lift up and I knew we were going over. We rolled about 250 yards, I'd guess. I'm just so glad that we didn't go across the median or clip the truck or hit somebody.

This could have been so much unbelievably worse! (and is was very baaaaddd!)