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+sleep
+=====
+
+Sleep is absolutely essential.
+
+## TOOLS
+
+[Sleep Cycle alarm clock](https://www.sleepcycle.com/). iPhone and Android app. Also see [How does it work?](https://www.sleepcycle.com/how-it-works/)
+
+## REFERENCES
+
+[Sleep](https://www.psychologytoday.com/basics/sleep). Psychology Today.
+
+[The Secrets of Sleep](http://ngm.nationalgeographic.com/2010/05/sleep/max-text). National Geographic.
+
+[How Sleep Deprivation Decays the Mind and Body](http://www.theatlantic.com/health/archive/2013/12/how-sleep-deprivation-decays-the-mind-and-body/282395/). Seth Maxon. The Atlantic. December 30, 2013.
+