Nightmares were long considered a fatal disease

The nightmare was long perceived as a medical condition in its own right with causes and treatments. Louis Dubosquet proposed in 1815 to replace the Latin term incubus with cauchemar in medical dictionaries. This doctor believed at the time that this nocturnal ailment could herald manic delirium or lead to death after repeated crises at the Hôpital de la Salpêtrière.