Depersonalization disorder may not be as rare as we think, affecting perhaps one percent of the population, according to recent research. It’s normally associated with an “unreal, spaced-out feeling you might get while severely jet-lagged or hung-over,” according to New Scientist magazine.
The sense of self has much to do with our awareness of our physicality and how we interact with the outside world. The brain integrates all the information coming in from the external world and from internal sensations and forms a default setting of "this is me here and now", says Nick Medford, who studies depersonalization at the Brighton and Sussex Medical School, UK. "If that setting changes somehow, then you feel 'not right', in a way that might be very hard to put into words."
There are probably several ways that change can occur, but Medford's work is looking at the emotional detachment characteristic of depersonalization. In people who have the disorder, areas of the brain that are key to emotion are much less active than normal, he says.