This is actually very common with everyone, PTSD or not. We develop our own unique way of coping and feeling safe in our lives. On many levels it has worked, therefore developing a better understanding or considering other ways of coping in healthier ways or different ways is uncomfortable and "risking what we feel and know about ourselves" that is just our own unique way of functioning.

As you actually open up more and make yourself available to learning and healing, you will not be losing your identity at all, you will instead develop new ways of functioning that will allow the "good part" of you to be better expressed and understood.