What the HELL just happened??!!??

That was what was running through my head as I was looking at my horse fully saddled lying flat on his side not moving.  (few minutes prior)  The day was going as normal as can be.  I got Steady out and tied him to one of my fence posts just like I always do.  I had all my stuff right there ready to go.  After his bath yesterday he was still shiney and spotless (gotta love a horse that doesn't roll the second he gets put in the pasture after a bath) so I didn't even have to brush him.  He was very mellow and he usually is when all of this goes on.  I put his saddle on, fiddled with it for a moment to check the fit.  He was standing perfectly calm.  I walk about 10 feet away to where my helmet was and started to put it on when I heard the commotion.  I turn around and he is fighting to break away from the post.  He then ends up on his knees with his neck stretch out fighting as hard as he can.  Then he grunts flips out and ends up on his side!!!  With his neck stretched out he really had no leverage to do much but he fought for a second and then just stopped and wasn't moving.  What was going through my mind..."What in the HELL just happened?!  Do I dare get close to him.  Well shit I have to try to pull the quick release knot.  I really hope I tied that right."  I walked up and pulled as hard as I could to try to get it to come loose.  It was pulled so damn tight from him struggling that it wasn't coming easy.  But it was coming loose.  That is when is started fighting again.  I yanked as hard as I could(after the adrenaline rush went away I realized I gave myself a nice rope burn on my fingers) it slipped loose and he was soon back to his feet standing there like nothing happened.  My heart was pounding I was shaking.  He is just standing there so I tried to move him forward because of course my first thought after that was, "did he hurt himself?"  As soon as I started to walk forward he lost it again!  He reared like a real rear I think he hit his head on a tree then he was back down on the ground with his two front legs and seemingly stuggling to get up.  It is strange where your mind goes in a moment like that, my thought process was, "What the Fuck(pardon my mind language)?  Did he break a leg?  He can't stand up?  Shit now I am going to have to call the vet.  I wonder how much costs to put my horse down?  I wonder if he broke my saddle?  Wait he is back up and standing on all fours.  WHAT IN THE HELL just happened????!!!!"  Once he was on all fours I got to saddle as quickly as possible to pull it off thinking that was the only thing that I could have done to cause this.

Standing there with him the saddle on the ground my heart pounding looking at all four legs to see if there were obvious injuries.  Which other than grass on his legs I saw nothing and wondering what to do next.    Well that was the end of the drama.  I walked him and saw short steps in his left hind leg and walked a little more and it went away.  I lunged him for a little bit and I think that there is some soundness problems with him.  I am guessing hocks because he is not showing obvious lameness but something is NOT right with my horse.  I think the lameness is unrelated to his psychotic episode but now I will be putting calls into the leg vet....sigh.  Sometimes I wonder if I can handle this.  I have no hard evidence as to what caused this episode and honestly he scared the shit out of me.  I don't know where we go from here but it wasn't where I had planned to go.