Hey hey @MaceWinduHugs, level 59 desu 
The answer to “Do I need to slow down” almost always is “yes” in my opinion, but you’re free to completely disregard this piece of advice and keep going really fast anyway 
Heck, even 20 lessons a day in some contexts can be “too much” and around level 50 you’ll go with 150 lessons on a level up. Good luck trying to nail them down in a single lesson session!
I made a terrible mistake of thinking I can always do lessons as soon as they show up and getting items to Guru as soon as it’s possible and and on January 7th I went through 725 reviews as a result of this 
I can still keep up, but that’s simply because for the time being I prioritize WaniKani over my actual job, which probably reflects itself on my performance at work too. What I can say is that if you’re going through 200+ reviews a day, or 100+ reviews in a single session, which is something I do almost daily, you start to autopilot and pretty often you just write in “cape” and press enter and never once even ask yourself if this is a cape like the one that superhero has or a geographical concept of a cape by itself.
EDIT: To give you the context of what I mean by “prioritizing WaniKani over actual job”, I wake up at 6.00am on Thursdays just to do lessons and reviews and barely make it in time before I start work at 9. I spend 6+ hours each Thursday and Sunday to get through the walls of items that and level up. I’m incredibly drained at the end of each day like that, but damn isn’t it rewarding
Not to mention putting the words in actual sentences. I know what 飽くまでも means, I don’t know how to use it in a context. I don’t have enough time to look it up, give me a break xd
Here’s the initial post of when I stopped being able to cope with reviews:
651 reviews in a day. About to become a norm. About to scream - WaniKani - WaniKani Community
Regardless of how many reviews I’m going through, I need to go through them because I can’t sleep with clear conscience knowing that there’s a review or two still waiting for me out there ;___; xd
The other advice in this thread, especially the one by @Rihn, appears pretty sound and I’d listen to his advice on that, what I could say is that Japanese is more than writing a few characters at a time and pressing enter each time you’re satisfied with an answer, try Bunpro, play video games, get yourself immersed, and most of all - remember to have fun along the way!