A case of narcolepsy is presented and the course of treatment described. Although the author found no answer for the question of how the libidinization of sleep behavior occurred, the function of the symptom was clarified. The patient used falling asleep as a defense mechanism which served to effect the hysterical restriction of self-perception ('inversion of activity'). In seduction situations which aroused the patient's denied sexuality, the falling asleep reaction permitted her an unconscious wish-fulfilment under the safe conditions of sleep. The latter served in this instance as a 'protector of the dream'.