It makes sense that you are having trouble since it is the end of the semester. College classes typically get harder as the semester (or quarter) come to an end. Your professor is preparing you for your Finals.

I think doing your homework would be fine, with lots of rest breaks. Just keep in mind that if you are struggling a lot, it might be a sign that you need to rest. In my own experience recovering from the concussion I sustained, if I had to struggle, there was no way I could retain that information. Your mileage may vary: meaning you may have a different experience.

When I need to rest, at this point in my recovery, more than 3.5 years after the auto accident I was in, I can either lay down and try to do nothing but sometimes that makes me restless. I have an iPad and playing a very simple but repetitive game, one that isn't really challenging, like Candy Crush, is a good rest for me. That way I am occupied but not pushing it - I hope that makes sense.

Any zen-like activity like that works for me. I can watch a simple TV show that isn't stressful for me, like New Girl of The Big Bang Theory, but I can't watch something that is going to be suspenseful, like The Following, because it makes me anxious and then it's not restful.

Coloring may also be a good activity.

Putting a puzzle together may also be restful.

Just don't get stressed out. If you start to get frustrated, then it's a sign that whatever you're doing isn't restful.

Make sense?