"pertaining to the state of consciousness when awaking from sleep," 1897, coined by English man of letters Frederic W. H. Myers (1843-1901) from hypno- "sleep" + second element from Greek pompe "sending away," from pempein "to send" (see pomp).

Hypnagogic — Illusions hypnagogiques (Maury) are the vivid illusions of sight or sound—"faces in the dark," etc.—which sometimes accompany the oncoming of sleep. To similar illusions accompanying the departure of sleep, as when a dream-figure persists for a few moments into waking life, I have given the name hypnopompic. [F.W.H. Myers, "Glossary of Terms used in Psychical Research," Proceedings of the Society for Psychical Research, vol. xii, 1896-97, supplement]

By hypnagogic paramnesia I mean a false memory occurring in the antechamber of sleep, but not necessarily before sleep. Mr. Myers' invention of the word "hypnopompic" seems to me unnecessary except for pedantic reasons. I take the condition of consciousness to be almost the same whether the sleep is coming on or passing away. In the dream I have recorded it is even impossible to say whether the phenomenon is "hypnagogic" or "hypnopompic"; in such a case the twilight consciousness is as much conditioned by the sleep that is passing away as by the sleep that is coming on. [H. Ellis, "A Note on Hypnagogic Paramnesia," in Mind, vol. vi, 1897]

1850, "the coming on of sleep," coined (as an alternative to hypnotism) from hypno- "sleep" + -osis "condition." But the distinction was not sustained, and by 1876 hypnosis was being used of artificially induced conditions.