I too had a couple bad experiences when I was younger... I've been riding since I was about 9 years old and for being young and small, I was frequently over-horsed because I was fairly talented right off. After years of being put on scary monster horses and jumping things I wasn't ready for, I suffered a few falls where I was banged up, scratched up, got a concussion or two and broke my tailbone twice. When my doctor said I wasn't allowed to ride anymore because of injuries to my back and hips, I gave into my creeping fears and simply quit riding.
A few years later, I began to miss the fun parts of riding (aka, the times when I wasn't scared to death) and decided to get back into it. Being a petite 5 foot 5, I wasn't crazy about giving into my cowboy dad's suggestion of riding my sister's 16-some hand monster. I decided early on that I was going to ride for me
, and not for anybody else. I sorted out my priorities and decided to purchase a pony that was for sale locally.
She's been the best thing for me. I feel totally comfortable on her and despite her quirks (like how she has unloaded me in about two seconds flat by slamming on the brakes and tossing her head), I actually am having fun for the first time in a really long time.
So basically, sort our your priorities. Getting on is good, but pushing yourself past what you can truly handle will only cause you to be a fearful rider. Let your trainer know what's going on and he or she might be able to put you on a trustworthy horse who will take care of you while you start from the bottom up in getting your confidence back. Horseback riding is supposed to be fun!
If it's not, you know you need to back off a little and get back to basics.
Ps- one-reign stops are very important on the trails