In common current usage, the term nightmare refers to dreams of particular intensity, with content that the sleeper finds disturbing, related either to physiological causes, such as a high fever, or to psychological ones, such as unusual trauma or stress in the sleeper's life. The occasional body movements seen in nightmares may have a use in awakening the sleeper, thus helping to avoid the frightening dream-situation. Occasional nightmares are commonplace, but recurrent nightmares can interfere with sleep and may cause people ...

Including:

• Nightmare - Historic use of term
• Nightmare - Notes

Read more here: » Nightmare: Encyclopedia - Nightmare

Nightmare was the original term for the state later known as waking dream (cf Mary Shelley and Frankenstein's Genesis), and more currently as sleep paralysis, associated with rapid eye movement (REM) periods of sleep. The original definition was codified by Dr Johnson in his Dictionary and was thus understood, among others by Erasmus Darwin and Henry Fuseli, to include a "morbid oppression in the night, resem ...

See also:

Nightmare, Nightmare - Historic use of term, Nightmare - Notes

Read more here: » Nightmare: Encyclopedia II - Nightmare - Historic use of term