Scientific research has shed new light on dissociative symptoms and dissociative identity disorder, formerly known as multiple personality disorder. This condition seems to arise most often when a vulnerable person meets a therapist with a suggestive line of questioning or encounters sensationalized media portrayals of dissociation. Research shows that people with rich fantasy lives may be especially susceptible to such influences. A new article published in Current Directions in Psychological Science, a journal of the Association for Psychological Science, suggests a mundane but surprising reason why some people might be vulnerable to dissociation: sleep problems.

The pop psychology belief is that patients develop multiple personalities to cope with traumatic experiences in their past, especially child sexual abuse. But this assumption isn’t supported by scientific evidence, says Steven Jay Lynn of Binghamton University, who cowrote the new paper with Scott O. Lilienfeld of Emory University and Harald Merckelbach, Timo Giesbrecht, and Dalena van der Kloet of Maastricht University in the Netherlands. Many people with dissociative disorders do say they were abused as children, but that doesn’t mean abuse caused their condition.

A more likely explanation, Lynn says, is that dissociative identity disorder arises from a combination of cues, from therapists and from visions of multiple personalities in the media. A vulnerable person can be guided by therapists who use hypnosis or ask leading questions, like “Is there another part of you who I haven’t spoken with?” Through that kind of suggestive therapy technique, people might start to think their mood changes, confusion, and impulsive actions happen because they have multiple selves living in the same body—when they begin psychotherapy with more run-of-the-mill psychological problems.

Lynn and his colleagues’ research further suggests that sleep problems may be one reason why some people are more vulnerable to dissociation and dissociative disorders. In one study, Lynn’s colleagues kept 25 healthy volunteers from sleeping for one night and found they had many more dissociative experiences. This could help to explain a connection between trauma and dissociation, as traumatic memories can disturb sleep. Poor sleep can also impair memory and increase suggestibility, potentially increasing the impact of leading interventions. “We’re not arguing that this is a complete or final explanation,” Lynn says. “We just hope the word will get out and other investigators will start looking at this possibility.”

“We want to educate the many therapists who may be strongly influenced by the traditional model of dissociation not only to think otherwise but to practice otherwise,” Lynn says. Therapists should “be scrupulous in avoiding suggestive approaches—not only with people who may be particularly vulnerable to those procedures, but with people in general who seek help.” Also, he cautions, “if your therapist is trying to convince you that you have multiple personalities, you should find a new therapist.”