Oddly enough, that has happened to me.
Fortunately I had a much better outcome. The back door of my trailer popped open, and the horse, Rosie, jumped out. It was a catalogue of woes, my keys and wallet had been stolen while I was out on a ride, and in the 5 or 6 hours it took to try to get the mess sorted, a well-meaning friend hitched my trailer to their truck and drove Rosie home. They closed the rear door, but I've always double-roped it too, thinking that the closure didn't look all that secure to me. The back door swung open and Rosie hopped out.
A couple of things that saved her were luck and design. She's not tied in the trailer, so she never got hauled along the road and broke her neck. Also, by luck, my friend had chosen the very quiet route home and the one truck that came along slowed and stopped (and caught the horse). The other route is a 5 lane crowded highway where everything is travelling at over 60.
I'm very concerned about trailer fastenings. When I first started trailering joePony in other people's trailers, I would always look at the closures with suspicion, but the owners would say, obviously, they're fine, it never comes undone ... Then I got mine, and just thought, you know, I am not convinced. Hence the double roping. It's a habit.
Mine is a very basic trailer, though, all the mechanisms on it are very simple and easy to see. I don't know what I would do if I ever got a 'better' trailer with more complex fastenings. Panic, I think.