Why is it I always get the greatest desire to learn things late at night when my body and brain are too worn out to handle it?
When I have the energy I can’t focus, when I can focus I don’t have the energy.
There have actually been studies about the not being able to focus when you have energy (I also have this problem).
The general suggestions include having a background distraction like music or a tv show/movie. It has to be something that will engage your brain slightly, but not drag your attention away from your main task. I will re-watch episodes from a favorite TV show or listen to music I love. In both cases, I know it enough that I can ignore it when I need to, but like them enough that they keep me slightly engaged.
The second one that works for me is a reward system that breaks up the tasks. So, I finish grading for one of my classes, then I go do something fun for half an hour or so, like knitting or spinning or computer gaming. I try not to spend more than an hour at a time on the not as fun task. If you are studying, you should make sure your fun activity is not mentally challenging. Your brain will continue to process the information you just read/learned for up to several hours after you have studied. This is also why people will dream about their homework.
Brains are weird.