A Clinical Study of Hypnagogic Hallucinations
British Journal of Psychiatry May 1, 1971 Carrick McDonald
Hypnagogic hallucinations occur as a person falls asleep and prevent deep sleep, while hypnopompic hallucinations happen upon waking. The distinction between them may be artificial because hypnagogic hallucinations by definition awaken the subject. Psychiatric textbooks vary in their assessment of these hallucinations' significance, generally considering them normal phenomena, with some exceptions.