Sweetie I know what you are going through, to an extent. I recently bought a 7 year old Hanoverian gelding for the price of gas to go get him...can you believe that? The reason for this was because he was a biter, kicker, man hater, would charge, rear, with shots he would rear and strike and was said to be dangerous, vicious and unpredictable. He was weeks away from being put down I found out later. He was spoiled as a baby so he didn't learn manners, as a yearling he was physically held down by 4 men while the vet gave him shots (only after the vet tried to twitch him and then chain him), he was put into dressage training at 2 where they would smack him with whips when he was "bad," as a 4 year old he started cross country jumping which he came away from being terrified of jumps and even ground poles, and his behavior was still so bad that the owner sent him to an equine behaviorist for a year. She tried to sell him so then she sent him to a college to try to be part of their dressage program and that's when things really got out of hand. He attacked one of the workers, bit and kicked a lot of people, and couldn't be trusted. And he was never turned out with other horses until he was 6 years old.
Sounds like I'm crazy, huh? I knew that's not who this horse was, it was just who he had to be to protect his dignity. See, this horse is very brave, confident and dominant. Horses like this are not afraid people are going to kill them. They are afraid people will take away their dignity. So they defend it will all they have. This is what my guy was having to do. I wanted a challenge for my next horse and I sure got it. I've only had him 7 months but the changes in this horse are incredible. He's so nice to ride now, I sometimes ride him barback with just a halter out in the corn fields behind our house. He's still got some issues but he has 6 years worth of walls to break down. He's like a Dr. Jeykl Mr. Hyde type personality. He is so darn sweet one moment and the next he's pinning his ears and acting like he hates your guts. When he does that I promptly drive him away and I won't let him come back until I have two ears full forward with a nice look on his face. And then he's fine. Back to Mr. Nice Guy. He's a very complex horse, pretty extreme in some areas but boy have I learned a lot. I'm doing a 4 day clinic with him in a couple weeks where I hope to get this attitude thing figured out. The clinician is one of my favorites and I know she will be able to give me some advice.
And for those who may be wondering, I've never been kicked or bitten by this horse. Shots are now a mild issue and he does not hate men:roll:
Sorry, I didn't mean for this post to be all about my horse....goodness!
Anyway, I would be getting a professional in there to help you. It sounds like something happened to trigger this. Horses don't just snap, unless there truly is something wrong with them. Good luck and stay safe!