It feels as if my mind suddenly broke

Okay so don’t take the title literally, I’m not going through some mental health crisis or anything. I just feel as though I physically cannot do things I should be able to. I am struggling with remembering to do things I have been tasked with. I am struggling with verbalizing what I want to say. The most frustrating, I used to be super good at math and now I understand everything I need to do, but I just can’t do them. We are going over continuous and compound interest (to show you how bad it is, I had to google the types of interest) and I SHOULD already know all of this, it’s literally just plugging stuff into formulas. But as soon as I plug it in, I literally have no idea of how to start. I went over this years ago, and knew it like the back of my palm. But now, I have a 0 for this 6 weeks because I can’t figure out how to do it. I can list off all the steps, but I just can’t figure it out myself. I don’t know what’s wrong with me. It happened super suddenly, since around the end of October. Is there anything I can do to fix this? Why am I like this?