Non-magic AU isn't really my favorite genre, but by the time I figured out this story was one (I mean, I knew AU, obviously, but . . .) I didn't care. I loved the banter between Harry and Severus; it's always nice when Harry can give back as good as he gets in that regard. And the characterizations in general are excellent. I think "a quick-witted man with a wide streak of bastard" may be the best succinct description of Severus Snape I've read to date, and while your Harry is less wounded--and less angry--than the canon version, he still has a rather endearing streak of semi-oblivious diffidence and insecurity. I'm glad he found the courage to take a risk and go after Severus. Oh, and gotta love a story where Harry gets the chance to--justifiably--call Severus an idiot without immediately being murdered. And you get extra points for including Luna and McGonagal. :)
The structure of the story, going back and forth between times, could have been confusing, but wasn't, which is an accomplishment in itself, and I liked the way you wove the sleep/lack of sleep motif throughout. And of course I'm a sucker for a hopeful ending. Well done!