Hi, nightmare can be due to postraumatic concussion . In many cases it is difficult to pinpoint specific causes of nightmares. Many people believe that they are simply due to random nature of dreams, however there could be a variety of factors that influence whether someone has nightmares and/or bad dreams. Following are the factors - Persons with anxiety, depression Persons who use drugs Persons with significant head injuries eating before sleep Persons who watch horror movies Persons with alzheimer disease , dementia Persons with psychosis Persons with sickness due to fever Sleeping in odd position Generally nightmares go away with time only thing these factors are to be modified. You are advised to consult psychiatrist . Thanks