This can result in partial or full amnesia and it is most common among survivors of traumatic events from childhood (but it can certainly occur with adults, too).
Fortunately, you do not need to remember what happened in order to heal. I know that goes against traditional psychotherapy training, but it's true - many people get better without specific memories.
They do the same things recommended in the book for people who do remember: learn and practice self-soothing techniques, use guided imagery for healing trauma, get exercise, body work, try moving meditation, use ritual and prayer, work with journaling and other forms of right-brain self-expression, see about temporary medication, and try one or more of the "alphabet" therapies, such as EMDR, EFT or SE.
It's important to make sure you go to practitioners who are sophisticated and experienced in dealing with PTSD and are informed about the wonderful range of (relatively) new and effective therapies that are available now.
All best to you and good luck with this.