I'm going to be more down to earth about this.
Your riding skills are the problem more than anything else. Or rather the lack of them.
You stayed on, and that is good, but a big difference in staying on out of dumb luck and sheer terror and staying on because the horse could not unseat you.
That is the root of your fear now. You know it was just sheer luck.
And you may have gotten in the habit of babying a horse too much, and making a pet out of it, rather than keeping it a horse. All the leading, talking and spending time with a horse, especially one new to you, will do is to spoil it to point of what you are seeing now.
And this will happen with even the best broke, most dead head horses too. The horses know when a rider/handler does not have a clue as to what they are doing.
If you are graining? You might want to reconsider what you are feeding horse. That can make a difference in how one acts. I've seen some be village idiots on oats. Perfectly fine when put on pellets, and vice versa too. Some do great with sweet feed, others lose their minds.
And sadly, since I think you said horse was underweight? This behavior may be the reason he was starved down. Many will keep a horse too thin because it cuts out some of the behaviors.
At this point, for whatever reason, you have a spoiled horse, that is fast learning that you can't control it, and will more than likely get worse if you don't get some help for both you and horse.
Lessons for you will help a lot, but in the meantime? Quit babying horse is you do, and be careful.
And while your friend may have more "experience" than you do, a lot of it depends on what type, and how good her foundation is too.
Horses make me a better person.
Last edited by Palomine; 09-02-2013 at 04:40 PM.