There's a wonderful New Yorker podcast about affintasia, which like other things accounted for much of my life.
Affintasia is when you can't imagine picture (recall visual or any sensory memories), thus they're aware of their past, but can't actually remember their own memories, feeling like you remember someone else's life story, the events foreign to your own memory.
It turns out that this can often to be triggered to various events (strokes, concussions or even … autistic spectrum disorders). And guess one, I've suffered from each.
However, I recall at one time when I had incredibly vivid dreams, which I can no longer do. Thus it seems likely it was the result of the one concussion (passing out and hitting my head on the concrete sidewalk). It was suggested then that it may affect my memory and when I complained on follow visits of no longer being able to visualize memories, he acknowledged that's often a symptom. But after that, no one ever followed up on it.
I've described how when I write, I can't actually describe my characters without finding a picture of someone with a similar body type and appearance.
And there's also a another version of hyper affintasia, where you can picture abstract concepts or creating entire realities, which are so realistic, they often can't tell the difference between their own imagination and reality (detached from reality, hyper-aware of their own creations).
It explains so much, yet leaves me wondering, once again, whether anyone on SOL has ever experience such conditions.