Why does my body react when I watch gory surgery or bloody scenes on TV?

Whenever I watch surgery on TV or a scene in a movie with alot of blood, (especially if it involves slicing, bone breaking or eye-gouging), my body seems to feel jelly-like in the same area that is affected on TV and if its particularly gory, all my joints feel strange, as if my bones are going soft. I know it is in my head, but why does this happen, does it have a name?