Welcome Perej,
I wouldn't say memory is at fault, but more the ability to pin down such an experience in anything concrete is what is at a loss. It is hard to also anchor it to a time frame, since you are within the present moment always, and that center-point is always used as a reference for being able to sense changes occurring among external things, including being able to see your inner change (among phases - evolutionary stages of mind) by sensing a difference in the way your interaction with the world at one point in time compares to another. From within, there was no change, and it cannot be detected directly, but the center has shifted.
Something of the sort also occurred to me around the time I first started meditating where suddenly my feeling a certain way or another was no longer automatic and dependent on the situation and mood, but on a choice, which itself stopped almost any emotional reaction, leading me to naturally question in a similar way you are, 'what's wrong with me?' Later on, I started to enjoy the silence in meditation, almost as a new sense of being, standing outside the constant mental noise I was accustomed to before, which in turn gave way to seeing more silent layers of noise manifesting as the mind wandering endlessly following trails of emotion-loaded memories and fantasies.
Your description about lacking of present awareness I can relate to, though I don't call it that but instead a greater tendency to speculate on things to the point of losing track of time. I cannot, however, say I've ever felt depersonalized, derealized, non-existent, having died, anxiety about it, and instead find my greater presence in the moment to provide both the opportunity to "be here now" and to somewhat ponder off into almost anything.
Do see the link Shanti gave to lesson 327. I found it immensely helpful when I first came across it.
All the best.
