I'm a nervous rider myself. I had a bad experience where a horse bolted on me and ran for 1/2 mile down the middle of a street. There was no stopping him. For some people this wouldn't have been a really big issue, but for me it was terrifying. It took me forever to get back on. I looked and bought myself a 16hh QH. I've had him a year now and I'm still working on my fear issues. He's a real loving horse and lazy. It takes a lot of coaxing to get him to even walk fast. I'm slowly building up to a canter, but not quite there yet.
The first time I "rode" after the accident, I had someone lead me around. I was so nervous. I thought I was going to pass out. But my horse didn't even pay the slightest attention that I was scared, he was acting his self as if I wasn't even there. Anyway, while I was being led around, we talked about different things. It helped calm me down. After my heart slowed and I was at ease, I felt accomplished even though I didn't actually ride by myself.