Everyday Vinyl Envelopes What Could Have Happened To My Back?

What could have happened to my back? - everyday vinyl envelopes

I vinyl siding for a living, and yesterday, slipped in a few cases on both sides, every day, and I felt a little pop in my back. When I felt a sharp pain pop on my buttocks and legs. I feel the pain now absolutely on the back is very stiff and I can not sit, they are planted my feet ..... Old can not sit directly on the bed ( "ideas", what happened?