I have never lost control while towing (knock on wood). But I did come close once. I had a small utility trailer full of firewood in tow, when it started to fishtail. I know that was due to the wood being loaded a bit too light on the tongue. I was on a stretch of road with a 65 mph speed limit, and I was doing about 55 when it started. I used the entire width of the road before I got it straightened out and slowed down. And yes, rearranging the load solved the problem.
So I have seen numerous trucks and cars towing and clearly having sway problems over the years. Many times the source of the instability is not obvious, but sometimes it is. Trailer and/or TV not level, obvious tail-heavy loading, tires overloaded enough to appear slightly flattened, I've seen each of these on the road. Good luck gathering data on why people have accidents.