I think if I hadn't been "forewarned" they would have gone through my windshield.
Had the same issue when a flatbed stacked with hay bails passed us on the left: “Sure would be lousy if that strap failed”, when it did. Hay bails bouncing all over, managed to steer out of it.
I have the same reaction as you did whenever I see some idiot moron driving down the road with mattresses strapped to the roof of their car.
I always think; “that’s gonna fly off”. And about 10 years ago it actually happened in front of me. And of course because I was thinking that it could happen, I was already taking evasive action and avoided running over the mattresses.
I’ve had similar things happen to me.
“Was behind a work van on the highway with a some ladders strapped to the top, I was just thinking “what would happen if those ladders broke loose?”, three seconds later they did and I was already slamming my brakes and cutting my wheels.”
I remember many years ago a contractor’s truck with lumber on the racks was going down the highway when an old lady slammed on her brakes right in front of him because she had missed her turn-off. The driver of the truck slammed on his brakes and swerved to avoid her but hit a car in the next lane, and the lumber came flying off and struck one of those small school buses (looked like a regular yellow school bus but a third of its size). Killed some kids. The old lady? Not a scratch, and swore it wasn’t her fault.
Worst one I had was a tire and wheel came off a travel trailer that I was following.
It came off and bounced about 10 feet straight up, then a couple smaller bounces, then ran true for a second or two, then started to wobble. finally, I went left, and it went right and bounced into the ditch.
I was on my way to business meeting with a co-worker gal in the passenger seat who kept screaming the whole time. I never took my focus off the tire so I could anticipate its next move. Like trying to average the swing in a pendulum or a plumb bob.
I was driving on the 101 freeway in LA and was behind a trailer with a boat on it, when the next thing I knew, the outboard motor had come off, hit the ground and flew many feet in the air, proceeded to fly over my car and nearly smashed into the car behind me. Luckily (looking in my rearview mirror) I didn’t see any other cars get hit.
This was 30 or so years ago and to this day, I am leery of driving behind boat trailers.