Most children are taught that the human body has five senses: sight, hearing, touch, taste, and smell. But many neurologists identify nine or more senses, and some list as many as 21.
The sense of touch is actually several "somatic" senses, including perception of pressure, heat, and pain, and there are also a variety of interoceptive senses, which analyze information that originates from within the body.
Interoceptive senses include balance (the sense of the body's alignment), the organic sense (the sense of internal condition, such as hunger or thirst), and proprioception (the brain's knowledge of relative positions of body parts).
Proprioception is the sense that is actually tested by walk-the-line or finger-to-nose sobriety tests.
Loss of proprioception, a rare disorder, can cause lack of coordination, and eventual complete lack of awareness of the body. It causes a disembodied feeling, as if the mind and body had separated.