I had my first and only fall thus far a couple of months after I started riding. I landed back first on a rock about 1/3 the size of my fist. Nothing broken, but damage to the soft tissue still causes me pain 4 years later - although it is no where near as bad now! It runs from my right lower back past my hip to the outside of my right thigh.
Riding usually causes the pain to flare up after about 45 minutes. Jogging for 20 minutes will cause it to swell up visibly about an hour later. The 2/week massage therapy I was prescribed for 3 months did nothing to help.
When riding, my lower back remains stiff, and horses tend to drift left when I ride. Mia is the horse I ride most of the time, and I think she has learned to ignore the extra pressure on her right side.