I have been trying to find it for the past 5 years or so, in vain. It's on fanfiction.net . One shot. I remember it vaguely. But I hope it helps. It's post war I think, every one's back for the last year or something.
Draco is alone, no more popular.
Draco is sitting by the black lake. Hermione happens to run into him. They have a civil conversation. And Hermione asks him "what is his biggest fear ?" To which he replies that "he's afraid he'd drown and die".
Conversations ends and they go back to their ways.
Few days later, Hermione sees Draco by the black lake sitting on some stone, from her Gryffindor tower's window.
She sees him jumping into the lake, afraid he might drown, she runs all the way from tower to the black lake.
When she gets there, Draco's nowhere in sight. She's shouting for him, thinking he drowned. But he gets above the water, and asks her what she's doing here.
She says she thought he drowned, reminding him what he told her the other day.
Then he says, that he's afraid of drowning doesn't mean he cannot swim. Some conversation and a kiss. The end.
Sorry for the long description but I hope you find it. It might not be a great piece of work but I love it all the same.