Sleepless but electrified Jordan says: "Function of 'reminiscing': to keep at bay sadness over what's lost."
What about sadness over what's about to be lost?
My senior year in college I remember experiencing what I can only call pre-emptive nostalgia: walking through the campus (this would mostly happen at night) I would imagine what it would be like to be making the same walk a decade or two hence, or, better yet, to be somewhere else remembering making that walk. Dizzying circle of projection: imagining myself as some future self that was imagining itself as the self I was at that time.
Experiencing that yesterday at Stanford, probably because I'd stayed on campus so late it was actually getting dark, which is about the only thing that can make the Stanford campus look romantic as opposed to the brash, vulgar, vastly scaled (though in a pretty way) place it is. Shadows were falling through the arcades and it was quiet enough that I could hear the palm trees creaking in the wind (in a non-romantic mood that would be pretty scary). The strangeness of making a conscious effort to store up a memory, which almost always has the exact opposite effect, but at the moment it creates heightened sensation and a sense of every detail's importance.