Never Lag Behind by Girl_Undone. Natsume napping on his desk was a common sight, one that everyone in class C had long since grown used to. (Although the teachers seemed to find it less and less amusing as time wore on.)
Status: 2 chapters. Complete.
I can't resist reccing a fic where the rest of Natsume's friends find out. I wish the fic were a tad bit longer so that they could have talked with Natsume more, but it's a nice little adventure.