If someone see my comment, there are many information here: http://www.supermemo.com/articles/sleep.htm http://www.supermemo.com/articles/sleep.htm It is really

If someone see my comment, there are many information here: http://www.supermemo.com/articles/sleep.htm http://www.supermemo.com/articles/sleep.htm It is really big so the best solution is to see it fast and read the summary. And it's worth it.