A condition between waking and sleeping characterized by illusions of vision or sound. These appear to have been first noted by J. G. F. Baillarger (1809-1890) in France and W. Griesinger (1817-1868) in Germany about 1845. They were studied by the scholar and antiquary Alfred L. F. Maury, who gave them the name "illusions hypnagogiques." They are distinguished from "hypnopompic visions," which appear at the moment when sleep recedes and momentarily persist into waking life. Both illusions are related to the faculty of dreaming. Some hypnagogic visions have been noted as the precursor to out-of-the-body travel or astral projection.
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