Nostalgia seems to be based a certain lack of awareness of one's experiences, that is, pre-narrative. Before we apply a frame, we experience "that stuff" of life without borders. Surely, we do have borders, but for nostalgic crooners among us (most of us), they were more porous and less intensely explicit.
Nostalgia is tricky, partially because we cannot recreate that time, especially and precisely because the notion of recreating it necessarily pollutes it. But also because the lathe of memory is too strong for us to remember accurately.
Nostalgia is like fantasy: best kept in one's head.