Please PLEASE help! In serious need.........???

2 days ago I got my 5 year old out to rie well not "out". But just riding her in the pature with a halter like a do sometimes. Granted she hadn't been ridden ridden just kinda lightly worked in the last 3 weeks every other day or ever 3 or 4 days. I got her halter on and hopped on. Started walking around in the pasture every thing was going fine, asked her to go into a trot every thing was okay she was listening, then BOOM! I asked her to go into a trot for the second time and she went into a bucking frenzy, I lost it on the third or foruth buck as I was bareback, I got up after I yelled a few words I will not repeat. Checked her back for pain checked her legs nothing she was fine, anyway. I got her out of the pasture today just to work on her, everything was going okay I got her to trot with no problem and walk with no problem. I wanted to take it easy as she seemed stiff NOT limping but stiff. So she started to lope I knew something was wrong right away. She loped three or four steps went into a bucking frenzy again. I hit so hard on the ground tonight I couldn't breath and we thought I had internal bleeding and are still waiting to see if I have to go to the hospital. As my mom is a nurse blah blah blah. After she threw me I wanted to get right back on, I even told my neighbor that came runnning and my mother and father I wanted back on right away. So I found her brought her back up and was going to get back on. But instead lunged her on the round pen until she was sweating(I let her have breaks). She then joined up with me........Which is a first for both of us. Anyway she is not in pain her tack fits I have checked her back her legs under her belly every where. There is no sign of pain or discomfert. She has never EVER acted like this. In the whole time she was being broken she only through me once. That was my fault though as I thought she was ready and I rushed and she wasn't. So I paid the rightful price for that. But i mean she is like a whole new horse she seems mean and just doesn't want near me anymore(well until we joined up tonight). No she is not in heat I have been watching since she threw me the first time. Did *I* do something wrong!? Could I have caused her to do this or? I have always been light with my hands and seat never have been rough. I don't know what to think. If it gets any worse or she seems worse I am gonna call the vet out and the chiro if the vet can't find anything wrong, to give her a check over. But I have no idea why she has acted like this.......Help please?