Sleep and Learning

Jonah Lehrer in Naps, Learning and REM :
"Numerous studies have now demonstrated that REM sleep is an essential part of the learning process. Before you can know something, you have to dream about it."
That is why, there is not much point in doing one semester courses in one or two week crash courses. But, when one has plans of using them immediately, it works differently I think. Similarly, it is easier to learn new stuff when one is working on a problem and the stuff seems useful. I guess that one should not depend on any one simple prescription.