When I was going through my counselling and subsequently the NLP training, I used to look on these forgotten/suppressed memories as being put in a big black box, locked away. Like Pandora's box, if you like, although mine were in a box, on a ship (ironically!), locked under a trap door in the hold.
But, sometimes these memories would find a way to rattle the box, rattle the trapdoor, remind me that they were there. And I learnt in the NLP training that actually that's the best time to consider opening the extremely scary box, because there's less to unlock.
Thing is though, that opening that box is very like opening Pandora's box - an awful lot of shit comes flying out, but there might be a tiny gleam of something pure afterwards. It is, however, possible to open the lid a tiny bit, let only a bit of the shit out, and then slam it shut - but that doesn't allow you to get rid of the box.
Another analogy (I like this one as well) - consider it's like a spot on your face. Not a blackhead, one of those godawful blind whitehead jobs. It's mountainous, painful, ugly, you keep poking at it - but if you try and squeeze it before it's ready, then you don't get all the shit out, AND you can cause collateral damage - more spots, scarring, bloody scabs etc. (Can you tell I'm a picker?
). Thing is, for that spot, or in fact any wound to heal properly, you have to get all the shit out. Otherwise, you leave a bit behind, it scabs over ok, but it's still there lurking underneath - never quite right. And then it erupts again later, when it's built up enough. And you go through it all again. But catch it at the right time, and all that disgusting stuff comes out - and you have a nice clean hole that will heal up properly. You might still have a scar - but the wound itself has gone.
Some people have more than one black box; or like in Harry Potter (Goblet of Fire), a box with many layers - so that you open one lid and get rid of some shit, but then you realise there's more shit behind another lid.
It takes a lot of courage to face whatever is in your black box, and good counsellors will help see you through opening them. But when those thoughts are knocking, that is still, IME, the best time to take a deep breath and have a wee peek.
I do like your therapist's disassociation explanation, Rumbling - that's really good.
My sister has no childhood memories, and I'm not entirely sure why, despite the whole thing I had with my mum - because she got on much better with mum than I did. But her whole childhood is a blank to her, except the very occasional thing, prompted by a photo or a film clip.