So today we started boarding a horse at my place. They were getting along pretty well (except for that my horse nipped the new horse on her neck not a big deal) my horse pretty much just showed his dominance. Anyway, everything was going fine, we fed them and they did great. But this night I went to get them both out of the stall (because it connects to the pasture) so they don't have a fiasco in there. By the way my horse eats in the stall and he was just finishing when I went in there the other horse eats in the middle of the pasture. So I went to go get them both out of the stall the other horse was waiting out side for my horse to finish eating and I was getting my horse out and then he went back in the stall when I was shooing the other hose away, and then I was getting my horse out the 2nd time (I was backing him out of the stall) and he just randomly charged and bit me very severely. When he bit me he hung on for awhile and knocked me over. I'm okay, just in a lot of pain. My horse has NEVER acted this way ever! He has never threatened to kick, or bite me or anything like that. We have a really good relationship and he knows I'm the boss. I have never even seen him act in a threatening manner towards anybody. He's the type of horse that will fall asleep with his head in your arms. I'm trying to figure out why he did this and what I can do to fix it. I don't want to get rid of the horse that's being boarded here, and I definitely. Do NOT want to get rid of my horse! Does anybody have any ideas on how to fix this, or as to why he did this? Thank you so so so much in advance!!! I know how serious of a problem biting is (because of how much pain I am in right now) and that is exactly why I want to get this taken care of as soon as possible. I just cannot understand why he did this to me. Thank you so so so much for any advice you can give!! Thank you!