How do i stop being so nervous?

I experienced the same thing with my own horse, I had had him since he was a foal, broke him in, rode him loads and never had a problem for about 5 years. then one day when riding in the fireld he bolted, bucking down the field, managed to stay on - just! but it really scared me. Finally after about a year or two I am totally confident with him again. I found that because he made me nervous, he knew I was nervous after that each time I got on him, which made him act differently. Just be brave and bold, dont be afraid to make him go forward, talk to him and show him you are not scared. I know it sounds silly, but it really did work for me. And I havn't had a problem since.