First of all, props to you for taking him and getting him the care he needs. Secondly, it's amazing what a horse can sense. I agree with what Doe said about confidence. If you're nervous, he'll probably be nervous... at least until he's back in riding mode again. 30 days with a trainer and some lessons on the horse in that time could do amazing things for both of you. You'll both get comfortable and he'll remember what being a riding horse is all about again.
Did you lunge him before you rode? It may seem minor, but my horse for example is unbelievably lazy, yet the first time I get on him, he gets lunged and lunged and lunged because that boy will play!! If I piled right on him, he'd probably do the same thing your horse did.
Best of luck to you!