Nightmares can be caused by a variety of factors, and the exact cause is not known. Some common triggers include stress or anxiety, trauma, sleep deprivation, certain medications, substance misuse, other mental health disorders, and certain sleep disorders such as sleep apnea and restless legs syndrome
. Additionally, reading scary books or watching frightening movies, especially before bed, can be associated with nightmares
. Some experts believe that dreaming, including nightmares, is part of the mind's methods for processing emotion and consolidating memory, but more research is needed to definitively explain why nightmares occur
