In February, Michael Boatwright awoke in a Palm Springs, California, hospital unaware of who he was. Even though he had been admitted to the hospital with a U.S. passport and a California identification card, he spoke only Swedish and insisted his actual name was Johan Ek. Photos tracked down by hospital staff several weeks later showed he had lived in Sweden as a child.

A psychiatrist diagnosed Boatwright with transient global amnesia in a fugue state—a combination of two types of amnesia related to memory loss and confusion about one's location. But while transient global amnesia lasts only a few hours, a fugue state can last for years.

The term "fugue state" was first used in the 1901 French publication Mental State Hystericals. The word "fugue," which means "running away" or "flights of fancy" in French, was used to describe a young woman who would have "hysteric attacks" and then act like a different person. She could recount these actions only when under hypnosis. When the article was translated into English, the French word fugue was used—and it stuck.

"Fugue state" has migrated to pop culture as well: A British newspaper wrote in July that tennis player Novak Djokovic, "who's been visibly shaken and playing second-rate tennis for at least the last hour and a half, somehow slips into this silent-killer fugue state."

David Spiegel, a professor of psychiatry and behavioral science at Stanford University, has worked with patients diagnosed with fugue state. He shared what is known about this rare disorder. (Related: "Remember This" in National Geographic magazine.)

So what exactly is a fugue state?

It's a form of amnesia in which the person forgets consciously various aspects of their identity. They often forget their current name, they forget their family connections, and they sometimes wander off and go on somewhere and start engaging in a new life for a while, without being consciously aware of who they were or where their previous friends or family [are]. It's a rare disorder, but it does happen.

I had one patient whose father had died, and he had a very conflicted [relationship with his] father and never really sorted it out. And he found himself on a plane going to England, which is where his father had been living before he died. And so it was an attempt to kind of revisit what had and hadn't happened in his relationship with his father but not one that he was consciously thinking through.

Why do they typically wander off instead of staying put?

The idea is that one of the stressors that may have triggered the fugue is something going wrong in the life they had before. So there may be conflict with a marital partner or trouble at work or getting into some kind of legal trouble.

So it may be that one way of resolving their conflict is to disappear and change identities.

What typically causes a fugue state?

There's usually some kind of life stress going on. They're in personal stress, marital problems, financial stress, legal problems. I know one case in which a woman found herself wandering around an army base ... even though she was not a soldier and didn't know who she was or why she was there. It turned out that her husband was on the base, and she had gotten letters from somebody who knew him claiming that he was having an affair. And so she found herself wandering around there.

They were reconciled, her fugue ended, so they got back together. So it can be that kind of acute stressor.

How rare is this condition?

This particular dissociative disorder is extremely rare, but I couldn't give you numbers. Most experts like me who treat people with this disorder have seen maybe five or six of them in their careers.

What does treatment usually involve?

It's actually a very difficult thing to treat. These people are often kind of stuck and don't particularly want to recover their earlier identity. I sometimes use hypnosis with them to try and get them to go back to a time before the change happened and see if they can recover memories of their earlier life and recover their identity. Sometimes it works, sometimes it doesn't.

There's no particular medication that specifically helps with it. It's management and trying to get them to learn about their previous life and help them figure a way to deal with the stressors that might have led to the amnesic episode.

Was treatment different for this disorder back when you treated your first patient versus now?

I'd like to say we've advanced a lot, but no, it wasn't all that different.

Is there any way modern science is able to uncover more about this?

In theory we could be doing some functional neural imaging and trying to see if there are specific regions of the brain that are working. We know now that many forms of amnesia and fugue occur because of an imbalance in relationships between two parts of the brain: the frontal cortex that can inhibit response and the limbic system, particularly the hippocampus, where we store and retain memories. People with dissociative disorders [such as amnesia] tend to have hyperactivity in the frontal cortex and less activity in the limbic system and the hippocampus in particular. So it's a kind of inhibition of memories.

In theory, that's what is going on in these people. The problem is we don't have them before and after [in brain scans]. We [only] have them after they've got it. In the future we might be able to better understand and perhaps manage the imbalance between these two parts of the brain.

How so?

We're now developing ways to stimulate certain parts of the brain and perhaps inhibit others, so in theory it might be possible to influence function in specific regions of the brain that might tip the balance and help them recover their original identities.

How short or long can a fugue state last? Is there a range?

It can either be for a couple of days or it can go on for years.

Is it possible for someone to fake a disorder like fugue state?

It's possible if you're a good actor and know something about the disease, I suppose.

Does this mental issue affect one type of person more than others?

We really don't know. Most of the ones I've seen [with this disorder] proved to be very hypnotizable. Not everyone is. So it's easier for them to slip from one identity state to another.

What does it mean to be more hypnotizable? Do you need certain personality traits to be more hypnotizable than someone else?

High hypnotizables tend to be people who are very trusting of other people. They are more intuitive. They get easily absorbed in events. They get so caught up in a good movie they forget they're watching a movie. They often have a history of either positive imaginative involvements with parents and others or physical abuse. So they've learned to use their minds to detach themselves either in a positive way or from traumatic circumstances.

And that seems to be something that someone in a fugue state would do?

Right.

How much do our memories define who we are as people?

A great deal. It's our body of experiences, and if we can't remember those experiences then it changes who we are. We define ourselves based on how we interacted with people and who we know and how they react to us. So an impairment in memory is bound to be an impairment in identity.