For a long time I've wanted to cut myself off and figure out a natural sleep cycle. Normally (for better or for worse), I sleep 5-6 hours a night during the week, then get 8-9 on the weekends, but that's definitely shaped to the work week.

Also, maybe interesting - two 4 hour sleep cycle with a couple hours between is what happens naturally to me after a night of too much drinking. I wonder if there's some reason for that.