That can happen when a person slips a disc, which then presses repeatedly on a nerve root in her spine. Her pain map for the area becomes hypersensitive, and she begins to feel pain not only when the disc hits the nerve when she moves the wrong way, but even when the disc is not pressing hard. The pain signal reverberates throughout her brain, so that pain persists even after its original stimulus has stopped. (Something similar, and even more drastic, happens in phantom limb pain, when
