This is a great question! I don't have any magic answers but I have a few suggestions:

1. talk to your T about what type of support he is willing to provide so if you go down the path of history and you get to feeling bad you will have a plan to fall back on ...like can you call him, email, will he call back, etc?

2. also I have had other people suggest to me, that it helps to talk about talking about it...if that makes sense... sometimes just talking about your fears and concerns about talking about the past reduces the anxiety...

I have the same issues that you do and I don't know how to access feelings or even some memories of the past but I imagine that if you share these concerns with your T he should be able to help you get there...

I've heard two philosophies on PC... one is to find the smallest thing about it that you can start with and build from there and others say take 20 seconds of courage and just blurt the horrible thing out and then you can talk about feelings....

let us know how it goes... I'm sure others will have thoughts to share as well