New horse fell down in the trailer! He seems fine but I'm traumatised.
We were almost stationary- we think he was bracing himself to move forward, but when we stopped and he tried to adjust, he slipped on some poo.
Once we got to him he happily waited for us to get the 2nd horse out and remove the partition, then he got himself up. We walked him around and he didn't seem injured. He was happy to load back up, and when we got home, he happily trotted around the field and then rolled. So I don't think he's injured.
I may never recover, though.
Thank god the person driving is an experienced horse owner and remained perfectly calm throughout the ordeal.