I have a bizarre personal anecdotal experience with spontaneous memory activation. I was leaving work one evening, and I'm recounting a dream from the night prior to a colleague as we left.
Suddenly, in what felt like an instant, I began to rapidly recall a chain of lucid dreams I've had. Dreams I hadn't remembered in years. I remembered not only the dreams themselves, but my life's circumstances when I had them. I describe this as a chain, but it felt to me more of a... portal. As if inside each of these dreams was a connection to the next.
I awkwardly paused, said a brief goodbye, and returned inside to look at myself in the mirror. My pupils were very dilated, and I felt like I was on psychedelics.
The strangest part is that this... connection has persisted. If I try to recall any of these dreams, including writing this comment, I'm unwillingly transported through these memories, and I have to consciously focus elsewhere.
No idea what to make of this, but it's definitely interesting.