Sleeping after learning improves consolidation of memory. Slow-wave sleep, which tends to occur in the first few hours after you fall asleep, is particularly important for memory consolidation. In one clever 2007 study published in the presitigious journal Science, subjects were exposed to an odor when learning a task. If they were exposed to that same odor during subsequent slow-wave sleep, their retention of the learning task was significantly improved. Here's the reference:
This suggests a simple aromatherapy technique to enhance your studying: infuse your study environment with a distinct, pleasant fragrance (for example, try an aromatherapy oil) -- then infuse your pillow with the same fragrance afterwards. During an exam or test, try infusing the same fragrance on your skin or clothes (just don't overdo it, or you might irritate the people writing their exams next to you!)
Furthermore, there is evidence that brief naps (60-90 minutes) in the middle of the day can help with memory consolidation, motor learning, and can also prevent the deterioration of mental and physical performance which tends to happen in a long day. Here is one reference about this:
There's a lot more research on sleep & learning. All of it supports the practice of healthy sleep habits in the life of a successful student. Many students have a very unhealthy, disrupted, perhaps heavily-caffeinated sleep schedule, particularly while "cramming" during the week of exams or other tests. This is hard on the body, physically and emotionally; it also leads to inefficient learning.
So, consider good sleep to be a component of your studying. And a nap after a bout of hard academic work can help you learn better.