Also, here is the deal on repressed memories, they are not as magical or mysterious as a lot of people act like they are.

First you should know that repressed memories were widely researched, understood and considered valid when the focus was just on war veterans. Most people in the psych field had an easy, straightforward time understanding how seeing your friend get blown up could be really traumatic. However, when the focus shifted to CSA/abuse survivors, suddenly a large chunk of the professional field started arguing against the notion of repressed memories. After all of the material I've read on the matter, I get the strong impression that it was a combination of two things:

1. The approach to the initial research had a big fallacy in it, which was that since repressed memories were happening in war veterans, experiences in war must be the only thing that can cause repressed memories. I mean, really, derp.
2. A lot of people were extremely uncomfortable with the idea that CSA could be as traumatizing as almost dying in combat. However it doesn't surprise me, psych professionals are humans, too, with their own dysfunctions, insecurities and secrets.

But you should know that repressed memories have been researched, understood and validated WELL before a bunch of freaked-out psych professionals started back-pedaling in the face of a very uncomfortable topic.

As far as how it works:

You have a lot of memories from your childhood stored in your brain, but they can't all be at the forefront of your conscious mind 24/7. You have experienced soooo many things throughout your life, formed sooo many memories, but you need to focus on a lot of stuff in the here-and-now to survive and function. You can't be thinking about 10,000 memories all at once. So you don't.

However, if you were in the grocery store and suddenly a song from your childhood came over the intercom radio, your brain would still have that memory of that song, and that memory would be activated and brought to the forefront of your conscious mind. You would probably like, "Oh wow, I haven't heard this song in 30 years! I completely forgot it existed!"

Memories repressed due to trauma work very similarly. The difference is that the reason they are not at the forefront of your conscious awareness, is because they were traumatic and your mind disassociated from them, stuffed those memories away. But the memories still existed down there, just like the memories of childhood songs.

Then just like the memory of the childhood song could be activated by hearing it in the grocery store, memories of a traumatic experience could be triggered by something that really taps hard into your subconscious mind. Also in most cases, several factors need to line up in order for memory to be activated, and not blocked by disassociation, at the same time.

As an example, Smells. The olfactory portion of your brain (smell processing) is strongly connected to your memory storage. Smells can often trigger even very old memories for this reason.