The other day in the car, I was listening to the new album Falling Objects by The Influence . In the lyrics to Old Bones, I heard Matthew Archer Stephenson sing "crawl into the nightmare" and became curious about the origins of the word "nightmare".
According to the Online Etymology Dictionary, the written word "nightmare" began in the late 13th Century. A Mare was "an evil female spirit afflicting sleepers with a feeling of suffocation." “Night” combined with "mare" was defined as an Incubus or Goblin that caused nightmares. In the Middle Ages, their existence was recognized by law. "Incubus", also from the 13th Century, was a male demon that had sexual intercourse with women while they slept. It was believed that having dream sex with an Incubus repeated times might even result in a women’s death.
The definition of "nightmare" shifted mid-16th Century from a Mare or Incubus to meaning the suffocating sensation they caused. Nightmare as "any bad dream" was first recorded in 1829 and as a "very distressing experience" in 1831.
Beware the Incubus and Mare still, for your dreams may be the death of you.