This used to bother me. I used to fear that all that is human would ultimately be lost and unknown to a cold and dispassionate universe.

It doesn't bother me any more, as my premise was wrong. I came to realise that the only way the universe can know us is through us - and that the best record of any moment is that perception of it lent there and then to those who lived through it - but ultimately the retrospective reminiscence of a gone past is but a pale shadow of the real, the here and now.

Cherish life, and strive for the future for its own sake - but never forget that what matters is here and now.

Come to think of it, I think what most fear is not death, but having never lived.

It's just a larger scale of leaving high-school (or leaving any significant period in your life behind). Things, people, problems from back then don't bother you anymore and you remember them only a little bit better than a novel you read, being out of context. Also you dive in nonexistence everyday when in deep sleep. And the universe winding down, well, like you said, its just an idea :-)