In Informal Learning, I noted that I seemed to do my best work while asleep. Berkeley sleep expert Matthew P. Walker has done the research that explains why this works.

Teenagers who get more sleep get better grades. Pull an all-nighter and memory capacity shrinks 40%.

During REM sleep, the hypo-campus is essentially emptied, enabling long term memories to link up and stick. For instance, if I'm learning poorly because I'm stressed, I'll do better once sleep washes the stress out of my consciousness.

 
Source: The role of sleep in cognition and emotion, Matthew P. Walker, The Year in Cognitive Neuroscience 2009

Sleep is yet another factor to include in creating an optimal learnscape.

In the end, the question appears not to be whether
sleep mediates learning and memory consolidation, but
instead, how it does so. The future of the field is truly
exciting, and the challenge to neuroscience will be to
both uncover the mechanisms of brain plasticity that
expand our understanding of sleep’s role in memory
processes beyond simple consolidation, into the con-
stellation of additional processes which are critical for
efficient memory development. Work across the neurohormones
sciences will be necessary to answer these questions,
but with the current rate of growth of research in the field,
the next decade should provide important advances in
our understanding of this critical function of sleep.

Thanks to Donald Clark's Plan B for tipping me off to Walker's work.