He calls it slacking off, I call it maintaining my sanity
http://www.medschoolhell.com/2007/02/19/five-ways-to-slack-off-and-still-do-well-in-medical-school
Great resource from medschoolhell! This blog is no longer active, but the archives still have some great info. Check them out once you have used these tips to gain some more free time.
