You may have situtional amneasia.. As you said "My next memory" hitting the horse was traumatic and your mind has blocked the memory of the events immed surrounding the "Crash".
Or, as others have suggested you may have a medical issue that can kill you fairly quickly and needs to be corrected before that happens.
Or. A less urgent issue.
So i would echo the suggestion to seek professional help (Doctor) for a good check up and make sure you hand him a copy of your original post (Easier to explain that way)
Now. On to the legal aspects.. A farmer has an obligation to do things like maintain fences and such to keep his livestock (horses included) from wandering into traffic.. SOME.. are, shall we say, a bit LAX in that duty.
Some, Despite their best (Very good in fact) efforts the animal escapes.
Some do not raise animals so they do not maintain their portion of the line fence between their back fence neighbor (Most places that portion is codified either in the deed to the ranch or local law,, Which hals depends on where you are). And the anmal escapes via the neighbor's farm.
IF it's a fail to maintain the Farmer MAY have liability for damage to your RV (And you) rather than you for the damage to the horse.
Just so you know.