Parts of the prefrontal-cortex of the brain are modulators of emotions. They can filter and suppress anxiety so one can work it out. They can also filter social pain to social exclusion, trauma so it is not felt to painfull. These areas are very active in depersonalisation and have stopped filtering but takes all emotions. That makes the emotional numbing. So, emotions isn't gone but they are not felt due to this mechanism. In depersonalisation it is thought that overactivity of the right ventrolateral prefrontal cortex makes the numbing and the sense of a loss self.