Horseback Riding fall? Sore!?

So I was walking my horse yesterday when he spooked out of no where. He bucked, and I lost a stirrup, and then he took off at a gallop. Needless to say, I fell off . However, I fell off right by a fence post, in fact, I think that's what knocked me off. My whole right side rammed into the post, and then I bounced off of it and face-planted. My face is scratched from the ground, but mostly my right side hurts. My whole shoulder feels like it's coming out of my socket, my back hurts, and I really think I might have bruised or even cracked a rib. So my question is what can I do to feel better. I have a lesson tomorrow, and I can barely walk. Also, how can keep my horse from spooking again. And please feel free to share your own stories about falls. Thanks!