Proprioception, also known as our
sixth sense, was the last of the senses to be investigated. In essense it is concerned with knowing where our
body is in relation to itself. For example when you close your eyes and touch your nose proprioception is what guides your movements. Without it simple tasks such as scratching the back of your head becomes almost
impossible.
In very rare cases it is possible to lose this sense - usually as a result of
drugs. When this happens the patient feels as if they are not attached to their bodies, they are no longer behind their own eyes. They must relearn movements using their eyes for
feedback. They also lose their sense of
balance, which makes walking extremely difficult.
For further (enjoyable) reading see
Oliver Sacks' book: "
The Man Who Mistook His Wife for a Hat".