One morning in 2008, Naomi Jacobs, then 32, woke up with no recollection of her previous 17 years. It’s as if the memories of drug abuse, bankruptcy and homelessness had been wiped from her mind. In fact, she says her last memory was of going to sleep as a teenager in the bunk bed she used to share with her sister, and of thinking about her upcoming French exam.

Eight weeks later her memories returned, but before they did, Jacobs says she had to negotiate the 21st Century world as her 15-year-old self. This meant learning to use “new” technologies like smart phones, but most challenging of all, it meant coming to terms with the fact that she had a 10-year-old son.

Jacobs’ incredible story is told in her forthcoming book Forgotten Girl and you can hear her talk in this BBC interview.

Split minds

From a medical perspective, Jacobs’ memory loss is considered to be a case of dissociative amnesia. This means there is no physiological explanation for why she temporarily lost 17 years’ worth of memories. Instead, the forgetting is psychological (or “psychogenic”), possibly brought on by recent or historical stress and trauma. Consistent with this, Jacobs says that not only had she lost her business and abused drugs in those forgotten years, she was raped at age six, and a boyfriend tried to strangle her when she was 20.

Dissociative amnesia is a controversial diagnosis. Some scholars, such as Harvard psychiatrist Harrison Pope, dispute that it really exists. They point out that there are no historical references to the condition prior to 1800. Other sceptics propose that the dissociative disorders (including dissociative identity disorder, previously known as multiple identity disorder) are not so much an automatic coping strategy triggered by trauma, but rather more a consequence of the patients’ expectations for how they ought to behave, prompted in part by therapists’ suggestions and fictional portrayals of illness.

Complementing this picture, people diagnosed with dissociative disorders typically also have diagnoses of personality disorders and emotional instabilities. They also tend to score highly in suggestibility and fantasy proneness. At the time of her memory loss, Jacobs was studying psychology, which may have exposed her to ideas about trauma and memory functioning. In an interview with the Sunday Times, she says she has “great reverence” for the mind. “I know that my way of dealing with trauma is for my mind to split,” she adds.