I started to learn to ride when I was ten. I had gotten good at my little pony, and the instructor decided to put me up on a larger fellow. He was led over, I stroked him on his face, and he took my pinky finger in his teeth. And wouldn't let go. I was then really scared of him, but had to ride him. To make things worse, I was really new at it, and didn't realize if I leaned forward he'd go faster. He broke into a gallop around the ring. And the instructor, instead of telling me calmly how to stop him, was yelling at me. It was three decades before I got on a horse again! I rode a pony on a trip, and he was crazy. They called him Poco Loco, but by then I was forty years old and had a lot more confidence. He tended to break into a gallop for no reason (except that he wanted to go home!) and I just laughed. Then, to really cap the experience, he bucked as I was getting off and I fell down. But I was still laughing!
My fear went further away when I met a new friend. She has a horse who likes to follow people around and nuzzle at them. He's a really gentle, funny guy, and I told her if I could have a horse like him I'd never be afraid!
Anyway, I don't know how to help, because I don't have a horse, and very little experience with them. But I sure do understand that background case of nerves, and wish you well in conquering it. :)