This is the 1998 BBC documentary entitled "The Man Who Lost His Body." The film follows Ian Waterman, who at 19 caught a virus that robbed him of his proprioception. As a result, Ian is unable to sense the relative positions of his limbs in space and whether or not they are in motion. The medical establishment believed that he would never walk again, but through sheer will-power Ian has been able to develop new strategies that enable him to function relatively normally.
The majority of movements and processes in a healthy adult are carried out unconsciously. However, because of Ian's disorder, he must deliberately focus all of his efforts on even the simplest of tasks (such as sitting up or displaying hand gestures).