Funny, on other forums I lecture others about the difference! Yes, full on real sway. Where it starts by one seeing the rear corner of the trailer peeking out on one side mirror, then over in the other, back and forth - and quickly progressing to much more... Luckily for me, a couple of scary times but not enough to loose control. Foot off the gas and applying the trailer brakes calmed it. I became hyper vigilant though watching for the corners appearing/disappearing in my mirrors!
BTW - weight on the ball makes the rear of the truck squat AND the "teeter-totter" effect of the rear axel takes weight off of the front wheels. With enough weight off, a full on "wheelie" with no contact of the front on the road at all. Of course, that is extreme....hence the WD system that moves that effect to both the front of the tow vehicle, and to a lesser extent to the axels of the trailer. Hence "restoring" some of the weight to the front end. The overall load doesn't change, so the vehicle still squats, just not all in the back. Saying that WD isn't needed in that situation is ill advised, as anyone that has overloaded in the rear can attest when they find their steering becomes marginal. (I'm thinking of my poor Chevy Nova from decades ago that had a load of bricks in the hatchback - almost NO steering at all in the trip home from the building supply....)