No, the disc doesn't slip. The discs are cartilage-like pads that sit between the bones of the spine and act like shock absorbers and cushions. When a disc is injured, the fibers of the disc bulge out, putting pressure on the nerves that come out from the spinal cord.

A small bulge may heal quickly and on its own, but a more serious injury called a disc herniation may take much longer. In this case the innermost fibers of the disc bulge into the outer fibers of the disc which in turn bulge out farther, again putting pressure on the nerves.