I had this very thing happen to me. Twice. Where suddenly any movement is almost impossible, the pain is so bad, and shooting down from the small of the back through the buttock and thigh. It took 4 trips to the chiropractor each time to fix things up for me. After the first session, it all still hurts, but you're mobile again, and after the forth, you're back to normal.
The trick is finding a good chiropractor who isn't also into quack therapies. They should just be back-crackers and maybe accupuncturists.
P.S. Playing CS:S is a good distraction from the pain, once you find a bearable seating position. I speak from experience...