Do you believe that you require 8 hours of sleep to be rested and effective. Well, in this really interesting article in the BBC News it seems like that pattern might not really be the most natural. Some experiments conducted came up with some interesting findings:
In the early 1990s, psychiatrist Thomas Wehr conducted an experiment in which a group of people were plunged into darkness for 14 hours every day for a month.
"It took some time for their sleep to regulate but by the fourth week the subjects settled into a very distinct sleeping pattern. They slept first for four hours, then woke for one or two hours before falling into a second four-hour sleep.
Though sleep scientists were impressed by the study, among the general public the idea that we must sleep for eight consecutive hours persists. More recently, the theory that humans slept in two distinct chunks has resurfaced, but in the rather less likely field of history." (from The Myth of 8 hour sleep)
If you are intrigued, here's the whole article.