You're not a fraud. The key thing in what you just wrote is that you were alone. There was nobody on your side. Imagine - if it's not too painful - if you'd had an aunt of a teacher who for years had given you a safe place to be where you felt welcomed, heard, understood and believed, even if they weren't able to stop the home situation. It would have radically changed your childhood experience and as such the pathways that were set up in your brain. You'd have known the bad stuff AND you'd have known what feeling safe and trusting people was like.
When you grow up in a situation not every getting those feelings of proper safety, it makes it hard to know who to trust, how and when, and you also do t grow up naturally understanding what it feels like to comfortably be part of a group (which maybe explains a bit the SA - I don't know, just a guess).
And flashbacks can be very physical, can also be smells of sounds too or even emotions (which is a total mind fuck).
I freeze, less now than before, but sometimes it was "just" internal and other times, embarrassingly, I'd be literally frozen mid step, somewhere public.
I've done a lot of EMDR which has worked with the individual triggers themselves (of which there are many) combined with something else that looks at how I have developed neurally to interpret the world (schema therapy is one, internal family systems is another) it's helping to reduce the symptoms.
But it's a fucking slow process and I apologise for swearing but the people who did this to me are not suffering, while my life is spent trying to escape what they did and I really think swearing is justified!
It can get better though.