Inability to determine one's true body position, motion, and altitude (or, in water, depth) relative to the Earth or one's surroundings.
It may result from a brain or nerve disorder or from limitations in the normal sensory apparatus. Most clues to orientation are relayed from the eyes, ears, muscles, and skin. The senses may not perceive gradual changes in motion and may overestimate the degree of abrupt changes and overcompensate when motion stops. Airplane pilots and divers also contend with apparent changes in gravitational pull, which can lead to dangerous situations and must be overcome by training. See also inner ear ; proprioception .