If a person has nightmares, it can mean they are experiencing nightmarish topics during their waking hours. For dreams can be continuations of what is experienced during the day. Trauma, which is prolonged stress, can be the cause of recurrent (repetitive) bad dreams. Trauma from the past, when unresolved, is likely to be the cause of nightmares.
If you have recurring nightmares, try this. Look for professional help. A psychologist/ therapist/ psychiatrist may offer a package of six consultations, to manage psychological issues.