Depersonalisation. The very word suggests a loss of personhood. But that's only part of the story of a complex and understudied condition that affects literally millions of people. And even after a century of investigation, most of these people still have never heard the term.

Depersonalisation can be a fleeting symptom of many disorders. But when it is chronic and unrelenting it becomes a syndrome in its own right- Depersonalisation Derealisation Disorder DDD . It is marked by an overwhelming sense of unreality and detachment from one's normal sense of self.

Depersonalisation affects a person's inner world of feelings, identity and thought processes. Derealisation affects one's perception of the outer world which can seem foreign and visually unsettling. Both are part of the same condition, appearing more or less at the opposite end of a fairly broad spectrum of symptoms that may include:

• Feelings of loss of self and embodiment
• Excessive self-observation
• Sensation of watching one's self in a movie
• Feelings of unreality
• Unreality of surroundings
• Emotional numbing
• Perceptual/sensory alterations
• Lost sense of time
• Existential rumination/obsessiveness