Depersonalisation as a defence mechanism.
If depersonalisation-derealisation began as a defence to intolerable negative experiences, it stays beyond its necessity as Depersonalization Disorder. In perpetually distancing emotion and awareness, it constantly obscures its own obsolescence.
DDD is stuck, perhaps still ostensibly protecting, despite all the damage to life that it itself causes and that any threats were long gone years ago. It precludes experiencing that all is safe now and that there are good ways to feel about the world.
Knowing such dynamics is certainly a help, though my DDD did not dissipate. Another paradox of the ‘defence mechanism’ purpose is that it leaves me more vulnerable, practically. Although DDD creates a ‘protective’ barrier to the world by rejecting it and my presence, in some ways it is also less of a boundary: the subdued and indistinct sense of ‘self-in-world’ means I am less secure and have more need for defence. Also, there is more need for vigilance when it is a struggle to sense the world around me at all. Of course, all that can drive more apparent need for DDD but I am watchful of such perpetuation.
Another vicious circle is if DDD symptoms themselves are seen as threatening and are then another reason for depersonalising. I do not react to my DDD like this, to me it is a horrible block and not scary, but it is understandable that it can be frightening (especially at first).