The condition which exits between the awake and sleeping states which is characterized by illusions of vision and sound. It was first recognized around 1845 by J. G. F. Baillarger (1809-1890) in France, and W. Griesinger (1817-1869) in Germany.
The state was studied by the scholar and antiquarian Alfred L. F. Maury who named it "illusions hypnagogiques." This condition is distinguished from "hypnopompic visions" which appear the moment that sleep recedes and momentarily persist in the awake state. Both types of illusions are related to the faculty of dreaming; however, hypnagogic illusions may be a precursor to out-of-body experiences.