It's all subconscious, of course. AK explains:
We do not need to ever KNOW what the original thing was, or the pains if they were pains, but we "revisit" the swelling darkness of it, and allow it to work its psychic dark magic on us.
What the memory or memories is or are is hardly the point. A common error when reading this is to imagine that we must REMEMBER, actually recall the specifics.
Instead, he argues, we should use the sensations/emotions that have been wrought in us in order to create something new. Do not try to recall the original event or whatever - you're writing, not self-psychoanalysing - but instead use the itch that has been created in you to explore something entirely new. It's all good advice. Alex is firmly of the belief that you should sit down and begin writing - not plot or research or plan or worry about this or that, just write. A character will emerge. That character will dictate the story. You just write it down.
Alex has run his online Boot Camp for a number of years, and has just re-launched it apparently. It's not for the faint-hearted - criticism is fair but direct- and it isn't free, but if you want to improve as a writer Alex can definitely help you.