The term alusia comes from the Greek verb aluein, which means to wander, to be distraught, to be beside oneself, or to be outrageous. It was introduced in or shortly before 1823 by the British surgeon John Mason Good (1764-1827) as a generic term for "illusions and hallucinations.
References
Good, J.M. (1823). The study of medicine. In four volumes. London: Baldwin, Craddock and Joy.
Dictionary of Hallucinations. J.D. Blom. 2010.