The sorcerous demons of Iranian mythology known as Divs are likewise associated with the ability to afflict their victims with nightmares. Signs and symptoms
Those with nightmares experience abnormal sleep architecture. The impact of having a nightmare during the night has been found to be very similar to that of insomnia. This is thought to be caused by frequent nocturnal awakenings and fear of falling asleep. Nightmare disorder symptoms include repeated awakenings from the major sleep period or naps with detailed recall of extended and extremely frightening dreams, usually involving threats to survival, security, or self-esteem. The awakenings generally occur during the second half of the sleep period. Classification
According to the International Classification of Sleep Disorders-Third Edition (ICSD-3), the nightmare disorder, together with REM sleep behaviour disorder (RBD) and recurrent isolated sleep paralysis, form the REM-related parasomnias subcategory of the Parasomnias cluster. Nightmares may be idiopathic without any signs of psychopathology or associated with disorders like stress, anxiety, substance abuse, psychiatric illness or PTSD (>80% of PTSD patients report nightmares). As regarding the dream content of the dreams they are usually imprinting negative emotions like sadness, fear or rage. According to the clinical studies the content can include being chased, injury or death of others, falling, natural disasters or accidents. Typical dreams or recurrent dreams may also have some of these topics. Cause
Scientific research shows that nightmares may have many causes. In a study focusing on children, researchers were able to conclude that nightmares directly correlate with the stress in childrens lives.
Since dreams are not predetermined, the brain responds to the situation by either thinking a good thought or a bad thought, and the dream framework follows from there. If bad thoughts in a dream are more prominent than good thoughts, the dream may proceed to be a nightmare.There is a view, possibly featured in the story A Christmas Carol, that eating cheese before sleep can cause nightmares, but there is little scientific evidence for this.Severe nightmares are also likely to occur when person has a fever, these nightmares are often referred to as fever dreams. Treatment
Sigmund Freud and Carl Jung seemed to have shared a belief that people frequently distressed by nightmares could be re-experiencing some stressful event from the past. Both perspectives on dreams suggest that therapy can provide relief from the dilemma of the nightmarish experience. Halliday (1987) grouped treatment techniques into four classes. Direct nightmare interventions that combine compatible techniques from one or more of these classes may enhance overall treatment effectiveness:
Analytic and cathartic techniques
Storyline alteration procedures
Face-and-conquer approaches
Desensitization and related behavioral techniques

Post-traumatic stress disorder
Recurring post-traumatic stress disorder (PTSD) nightmares in which traumas are re-experienced respond well to a technique called imagery rehearsal. This involves dreamers coming up with alternative, mastery outcomes to the nightmares, mentally rehearsing those outcomes while awake, and then reminding themselves at bedtime that they wish these alternate outcomes should the nightmares reoccur. Research has found that this technique not only reduces the occurrence of nightmares and insomnia, but also improves other daytime PTSD symptoms.