"The thing that people experience as 'fugue state' does happen," Ongur says. "There are people who wake up in other cities and don't know what has happened."
The fugue state is actually part of a larger family of conditions known as dissociative memory disorders. The trigger for these conditions is usually a traumatic event -- the death of a loved one, for example, or an extraordinarily stressful event at work. It is also more common in those who bear past trauma from events like natural disasters and war.
Chronic Fatigue Syndrome, or CFS, has garnered additional support as a legitimate diagnosis in recent years. Today, the U.S. Centers for Disease Control and Prevention (CDC) recognizes it as a condition that affects between 1 million and 4 million Americans.
Of these individuals, according to the CDC, only about half have consulted a physician for their illness -- even though it has been known to cause serious impairment in some.
As the name implies, CFS is most often associated with severe, debilitating fatigue. Non-specific pain and other symptoms are also common hallmarks of the condition, which is disproportionately experienced by women. As the condition persists, patients will often become depressed at the current lack of proven treatments to remedy the problems they experience.
But while the condition is starting to receive more attention and support, the underlying causes largely remain a mystery. Some have cited Epstein-Barr virus as a likely culprit. Others point to anemia, while still others implicate allergies.
Perhaps it is for this reason that the borders of this diagnosis remain contentious at best. Symptoms run the gamut from long-lasting flu-like symptoms to memory loss. Treatment can involve antidepressants, antihistamines or acupuncture.
To Hadler, CFS seems less like an actual condition and more like a rapidly growing hodge-podge of symptoms associated with a number of different diagnoses that are becoming increasingly more prevalent.
"Now it overlaps with post-traumatic stress disorder, fibromyalgia -- all of these labels include symptoms of fatigue," he says.
Still, dozens of studies -- many federally-funded -- are seeking answers as to the true nature of this condition.
It's been the stuff of horror movies and big-screen comedies. Yet, the truth behind Multiple Personality Disorder -- or Dissociative Identity Disorder (DID), as it is known today -- is, in most cases, a far cry from these dramatic interpretations of this classic psychological condition.
"Even when a patient says it's a different personality, it's nothing magical," Ongur says. "When people describe it, it is really a very extreme version of the more familiar feeling of disintegration. If you are under extreme stress or have had certain past experiences, the way the mind functions may actually break down."
Those who experience DID will create at least one "alter" personality that manifests itself in certain situations -- in essence, "taking control" of one's personality. These changes occur involuntarily, and DID in its most severe forms can limit one's ability to interact with others.