(CNN) — After a traumatic event, people often relive the experience in their dreams.
Survivors of serious car and motorcycle accidents still have nightmares about them months later, one study found, and these recurring dreams were linked to long-term sleep problems. Another study reported that about 21% of women who were victims of sexual or physical assault experienced nightmares three months later, and those who were having such dreams were more likely to develop post-traumatic stress disorder.
It doesn’t sound helpful, but there is a flipside to these findings: Nightmares in the first few weeks after a traumatic event have not been associated with health problems, and experts think they could actually be beneficial.
“We think nightmares are so common that they have some purpose to process stressors,” said Anne Germain, director of the Sleep and Chronobiology Center at the University of Pittsburgh.
In the overall population, about 85% of adults report having at least one nightmare in the last year, and 8% to 29% have monthly nightmares.
“That’s OK, but if you have them once a week or more, it usually bothers people, and it can be a problem,” Germain said.
There is no evidence to support specific benefits of nightmares, Germain said, and nightmares that continue can have some ill effects on health.
“There are plenty of data supporting the idea that nightmares that become chronic are very detrimental to well-being — sleep is disrupted, we think about dreams during the day and become distressed,” Germain said.
In the motor vehicle accident study, 25% of victims were having nightmares two weeks later, but in the time relatively soon after the accident, they were not associated with long-term effects on sleep quality. By three months after their accidents, 19% of survivors still had bad dreams; that’s when they were linked to problems falling and staying asleep and not functioning well during the day up to one year later.
Nightmares: the body’s check-engine light
“Nightmares are a replay of a traumatic event, so it is kind of like your body’s own exposure therapy,” said Michael Nadorff, assistant professor of psychology and sleep behavior medicine specialist at Mississippi State University. Exposure therapy involves having patients confront situations or things that scare them to help them overcome their fears.
“(But ) within a month of trauma (which could be anything from a physical assault to the loss of a loved one), nightmares are healthy … it’s helping you come to terms, and (realize) that’s over and done with, it’s making that memory less jarring,” similar to the goal of exposure therapy,” Nadorff said.
“After a month, nightmares are not healthy (and) usually for the people that still have nightmares, it’s not going to get better on its own…it’s like a broken record.”
Research suggests that chronic nightmares can actually keep people from recovering from trauma, Nadorff said.
“For a lot of people, it’s an early warning sign, like a check engine light,” that you may need help recovering from a trauma, and also that you may potentially have a bigger problem, such as depression or anxiety, he added.
Treating chronic nightmares
When nightmares become a problem, there’s evidence that a practice called image rehearsal therapy can banish bad dreams, Nadorff said. The therapy is based on thinking about nightmares during the day and recasting them with events, people and places that are less threatening. People think through these edited nightmares for about five minutes twice a day, which can be done on their own or with a therapist. The goal is to stop having nightmares or even to substitute them with a new dream.
One study showed that image rehearsal therapy helped women who had been sexually abused, and who had been having nightmares for about the last 15 years, reduce their nightmares, improve their sleep and and also reduce their post-traumatic stress disorder.
Alternatively, a blood pressure medication called prazosin is as effective as image rehearsal therapy at reducing nightmares and improving sleep quality.
It is up to patients whether they would like to use therapy or medication to treat their nightmares, Germain said.
Even in cases where nightmares become chronic, they have a bright side, and that is to reveal things that may bother you that you didn’t even know about.
“If somebody starts having bad dreams, and didn’t go through a trauma, maybe there is something that we are actively avoiding that is really bothering us, so that might be a cue to pay attention,” and to be more aware of emotions during the day, Germain said.
