That would have been my first guess.
I don’t have any advice that wasn’t already given but I’m in the same situation right now, maybe hearing from a fellow sufferer helps too
I just went to Japan for 4 weeks but still kept working at night in my usual timezone so I was pretty busy and always tired. Just before I left for Japan, I had picked up my level pace from around 12 days per level to 7 because you seem to see everyone here doing it and I was impatient and wanted to finish everything soon. And I wasn’t willing on giving that up just because I was going to Japan. Moreover, I was too stubborn to enable vacation mode (I did enable it twice after I was already drowning in reviews but always disabled it shortly after, thinking that I’m just wasting time; haha, what a great idea that was).
Now I’m sitting here with a hundred lessons and 450 reviews and I’m getting pretty much everything wrong. And every day I fight my way down to 350 and I think “tomorrow I’ll be down to 250!” and then I come back the next day and am back at 450.
Yesterday, I almost reset down to a lower level. If it wasn’t for the confirmation email that I received. If it wasn’t for the carbigators friendly words:
Most people reset their accounts because they’re feeling overwhelmed. It is possible to chip away at your review queue and let SRS balance everything out if you’re having doubts about this reset.
I would have gone through with it but I stopped. And now I’m back here, doing 50 reviews at a time and no lessons. And I would lie if I said that it was fun. It is not, I don’t like it at all, it feels like a burden. But I’m sure that if I slow down and give it some time, it will be OK again eventually. I once had a slow level that took me 52 levels because I was just drowning in work and barely sleeping and I also got back on the horse after a while. And I can make it this time too. And so will you, you already made it so far!
I think I was focusing on WaniKani a bit too much. It does a very good job at keeping you motivated and coming back. Which is nice and all but grammar, other vocab and reading & listening are important too and I feel like I’m neglecting them a bit. I think after I’m back on track I will aim for a relaxed 14 day level up time (if I can beat my unhealthy desire to race it as fat as I can) and try to focus more on other resources too. It doesn’t help being able to read all the N5 kanji if I still struggle with other basics.
Sorry for the wall of text. I obviously also needed a bit of an outlet for my burn out-life got in the way and I was being stupid and biting off more than I could chew-pain. We can do this!