Repeated nightmares involve a reoccurring theme in a series of bad dreams.

Nightmares begin in childhood usually before the age of 10 and are considered a normal part of childhood unless they significantly interfere with sleep, physical development, or psychosocial development. They tend to be more common in girls than in boys.

Nightmares may continue into adulthood. Nightmares in adulthood are often associated with outside stressors or exist concurrently with another mental disorder