It's pretty well accepted that sleep is good for learning. (As previously discussed by me.)
Last night I had my first final in Sports Law. Every semester I have post exam stress disorder, most frequently in the form of dreams, as I've described here and here. I felt pretty excellent coming out of this final, and there was very little anxiety over it.
Nevertheless, last night I distinctly remember being in a quasi-sleeping/dreamlike state: I was rehearsing the names of cases from Sports Law and reviewing what they held. To me this represents direct evidence of my brain at work while I sleep! Amazing!
The best part is that I half-woke from this midnight review and, aware of what I was doing, promptly scolded myself: 'That final is over! No need to learn those cases, kid.'