“A dream is invariably an attempt to get rid of a disturbance of sleep by means of a wish-fullfilment, so that the dream is a guardian of sleep”. Sigmund Freud (1940/1953) According to the classic theory framed by Sigmund Freud, the basic and teleological function of dreaming is to protect sleep from disruption (Freud, 1900/1953); a quite rational hypothesis since sleep constitutes a vital need for living species (Kryger et al., 2011). This aspect of Freud's dream model—which as a whole is considered as the initial cornerstone of psychoanalysis (Laplanche and Pontalis, 1988)—leads to two empirically testable conjectures, thus allowing its scientific examination: (1) arousal during sleep triggers dreaming; and (2) non-dreaming causes sleep disruption. We review here the experimental, medical, and neuropsychological data which allow testing these two conjectures; in this paper, the term “significant” denotes statistical significance at the p < 0.05 level.