I'm doing 100x better now than I was this morning.
I struggled and struggled and finally I managed to find a chart in my notes that my mind could grab onto. From there, I found myself able to concentrate on some other things--and now I'm doing what I'd planned to do yesterday, listening to my professor's lecture for this week.
I'm halfway through now.
Now my mood is completely normal. I was really whipping myself into a frenzy earlier!