The cause of recurring nightmares is the interaction of personal disposition and acute triggers.
Genes
Since several years it is known that the disposition for nightmares is partly inherited. If one identical twin is suffering under nightmares the other twin is likely to do so as well. With fraternal twins it is less the case. This is an indication for the joint responsibility of genes in the emergence of nightmares.
Personality
Scientists assume that sensitive and creative persons are more likely at risk. Irritable, fearful or depressive personalities seem to be more prone to nightmares as well. Persons who suffer under an anxiety disorder or an addiction often have a worse sleep and more often have nightmares than mentally healthy people.
Medication
When taking medication always carefully read the package insert. Nightmares are a possible side effect of numerous drugs, like remedies against high blood pressure and Parkinson’s as well as several serotonin reuptake inhibitors (a wide spread form of antidepressants).
Stress
One of the most common causes of nightmares is stress. Stress at work, at school or in the family might be burdensome. And the daily events might become part of the nightly dreams.
Traumata
Traumatic experiences like war, accidents, rape or natural disasters often trigger post-traumatic stress-disorders (PTSD). One significant sign of PTSD are nightmares. People concerned react much more strongly on nightmares than healthy people. It might be possible that they startle with palpitations. They need a long time to go back to sleep again. In case traumatic experiences remain untreated, nightmares might become a constant, maybe life-long, burden.