My first thoughts seemed to run with RP's.
It's probably a touch of ......sadness. That sense we have when things are changing and we know (or believe) that things will never be quite the same. It's similar I think to nostalgia, which we all seem to get a taste of from time to time.
It's not 'bad'. Change is part of life - right. And there's no telling that the future won't hold things that are even more exciting. But we can't "look back" on the future.
I'd say sit with it - but don't over-absorb it. Like anything nostalgic. It's like strong drink. A little won't hurt - may even feel good. Too much can kill ya.