If nightmare occurs when sleeping, there are several factors as follows: 1, the most common factor is the abnormal discharge of brain wave, patients who have had epilepsy or Parkinson’s disease in the past, the nerve nuclei of the brain cells will have abnormal discharge from time to time, and nightmare occurs when the cerebral cortex is abnormally discharged when sleeping. 2, there will be a certain stage of light sleep before people enter deep sleep, and nightmare occurs when people enter the stage of light sleep, and nightmare often occurs among people with vegetative nerve function disorder or those who are overly nervous at work. It often occurs in people who have vegetative nerve function disorder or who are overly tense and anxious at work. Because their light sleep time is prolonged, nightmares will occur.3. Transient cerebrovascular ischemia and spasm attacks will occur during sleep, which will also lead to nightmares during sleep.