A nightmare is a dream that can cause a strong negative emotional response from the sleeper, typically fear and/or horror. The dream may contain situations of danger, discomfort, psychological or physical terror. Sufferers usually awaken in a state of distress and may be unable to return to sleep for a prolonged period of time.
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nightmare An unpleasant dream which evokes feelings of fear or horror.
nightmare A situation resembling a terrifying dream.