What is proprioception? What does losing it prevent you from doing?

Proprioception is a 'sixth sense' that allows humans to internally monitor their physical movements. The sense is enabled by the coordination of several bodily systems so that monitoring one's movements and physical position is a largely non-conscious process. Losing proprioception makes it extremely difficult to do almost anything and to move very generally. You have no sense of where you are, whether you're standing up, sitting down, etc. People with proprioception often have to use their eyes to monitor their physical position and movements.