I hit a slump this summer. I was on the same level for more than 2 months.
I recommend not doing any lessons, only focus on slowly, slooowly but surely catching up on your reviews first. Doing lessons will only make that hurdle higher while you’re in this slump. It might feel like ‘giving up’ to stop lessons, but trust me it’ll make catching up on reviews a lot more doable.
You will get many reviews wrong. I know how frustrating that feels. Don’t worry about it! I try to think of it this way: if I got a review wrong, then it’s GOOD that I will have to review that item again sooner. It’s what my brain needs.
Everyone has to find their own reasons in life to do things that are hard, I believe. For me, my reason to keep it up with Wanikani, is that I have been able to really notice that I CAN find those kanji it’s teaching me, in the real world. It’s very re-affirming to run into Wanikani kanji and vocab in every day situations. However, if you are level 18, perhaps you might not run into those instances as much, so you should keep looking for your own reason right now!
And look for many reasons, not just one. BennetTheSage made a video about trying very hard to lose weight, and the things he says about it in this video resonate a lot with me and the slog of learning 2,000 kanji. Maybe watching the video will help you too. [here’s the video]