A nightmare is an emotional assessment of something that frightens, scares or annoys. The word is more often used not as a synonym for the word horror, but as a condemnation by a person of any circumstance, as an emotional expression of disapproval and anxiety.
The whole yard was dug up, all the lawns were spoiled! Some nightmare!
Nightmares — disturbing dreams, causing a feeling of fear.
Usually a dream in the form of a nightmare takes on explicit plot forms, with the dreamer himself at the center of the plot. The plot can develop in the form of persecution, a series of any accidents, in which the dreamer usually becomes a participant — but at the very last moment he wakes up. Much has been done by the school of psychoanalysis, including Sigmund Freud, to explain the effect of «night terrors».
In mythology, a nightmare is often associated with some otherworldly forces. Nightmares can become the subject of literary works and horror films, such as the movie A Nightmare on Elm Street.
Less commonly, the word «nightmare» is used to refer to some monstrous, terrible phenomena that go beyond the reasonable and rational, occurring as if in a dream.