Time ago, I read an article that explained some curious and really usefull "not much knowed" things about our spanish contribution to the world: the siesta.
I've read that siesta improves our learning process and also our long term memory. In addition, it told that if we sleep after studying, we'll memorize better the studied thing, because we would have eliminated disturbing influences.
I knowed something related to this, but I didn't remember that I have that importance. We have many "needs" that demand us a big and progressive mental effort, so some times we could underestimate the sleep just to satisfy them. But the reality is that if we don't sleep enough, we'll learn slowly and it'll be more difficult. I know that's hard to sleep always our 8 hours, because we can do things at night that we can't in day, or just because we want to extend the day. I'm not the most appropiate person to say this, I love to go to sleep late, I like to see the darkness of my street with his fresh smell and the sheen of the moon... and also because I'm more calmed, relaxed and inspired in late hours than in early hours. I would like to have more "free" time to sleep calmly, or to satisfy some "needs", but we all are imprisoned in a cultural prison... but I'll talk of it later, when I'm more inspired.