maybe this will help in understanding how a person with anxiety\ptsd can get depersonalization....

here in the USA depersonalization \ derealization problems are ...feelings....

feeling spaced out,
feeling numb
feeling like you are moving in slow motion
feeling like you are moving too fast
feeling like everyone and everything around you is either moving too slow or too fast.
feeling like you or the world around you is not real

sometimes when people have panic attacks their panic attack makes them feel spaced out, foggy, numb, and all those things I listed.

heres an example. I have a fear of high places. I climb a ladder and I start having a panic attack (worry that Im going to fall, trouble breathing, heart pounding) I close my eyes and notice I feel numb like, i cant feel my body, I know my body is there I just cant feel my fingers holding on, nor my legs holding me up. my brain has stopped thinking just holding on for dear life until i can find a way down.

once I am down off the ladder I start feeling again, start thinking again, and notice my legs feel shakey.

thats how a person can have a panic attack and have depersonalization at the same time.

because people can have depersonalization\derealization problems with their PTSD this problem is now one of the diagnostic criteria for having PTSD. people can now have PTSD alone and they can have ptsd with depersonalization\derealization symptoms. the diagnosing treatment provider "specifies" whether or not a person is having depersonalization \derealizaiton problems with their PTSD or not.

my suggestion is talk with your treatment providers, they will explain to you how you can have these problems all together. and what symptoms you had got you diagnosed with them.