I thought about this more on my commute home from work, and I'm starting to suspect that "SDAM" might essentially be the long-term effects of alexithymia or interoceptive blind spots, which are fairly common in neurodivergent people with ADHD, autism, or both.
For context, alexithymia is a significant difficulty in recognizing, sourcing, and describing one's own emotions. Interoception is the sense of your internal bodily state.
You can likely relate to being so deep in a flow state that you don't notice how badly you need to use the restroom, or how hungry you are, until the feeling becomes so overwhelming it finally breaks through your focus. That's an interoceptive blind spot in action.
So, to further elaborate on my theory: If alexithymia raises the required signal strength for an emotion to be consciously recognized as significant, our brains - which strive for efficiency - will only tag and store memories that cross that unusually high threshold of "important." All the "little things," even the nice ones, get dropped because they never registered with enough emotional weight at the moment they happened.
The brain prioritizes emotionally significant information for memory storage. If an event doesn't trigger a sufficiently strong or clearly identifiable emotional response at the moment it occurs - because your baseline emotional processing is affected - it might get stored as just factual information rather than a rich, emotionally resonant autobiographical memory. It becomes "a thing that happened" rather than an "experience I had that affected me emotionally."
This explains my memory pattern perfectly: I remember most big family holidays - Christmas, birthdays, weddings - because those come with heightened emotional anticipation and distinct social components. But I'm already struggling to piece together what we did on Easter this year, and have absolutely no idea what we did last year. The quieter, more routine positive events apparently don't meet that higher "emotional importance" threshold for deep encoding.
It's like having a filter that's calibrated too conservatively - it's protecting you from information overload. Perhaps that's why it's so common in neurodivergent people, both ADHD and autism heavily affect how we take in and process external sensations. If there's any positive spin to this theory, that I will agree with you, makes sense in a not good way, it might be that. But, unfortunately, it's also discarding experiences that others would naturally encode as meaningful memories.