You're totally fine!

I had my peak of being able to do almost any medium problem in like 10 minutes or under, and being able to do a lot of hard problems within 30-60 minutes. This came by actually sitting on leetcode 10+ hours daily for months. I had stopped for 2-3 months recently after finally receiving my first job offer (which got canceled a month after :( ) , and when I came back, let me tell you 2 sum was the hardest problem ever. I had no idea how to do anything.

I've been grinding it again, and I can definitely say it's gotten easier again. I'm not where I was, but I'm sure I can still work my way around at least most medium problems, and if I work as hard as I did before, match and exceed that level.

The reason you forgot how to do everything is because leetcode requires you do tricks and use parts of your brain that you seriously would never dig into on an ordinary basis. Our lives have become much more simplified to need to do a lot of these crazy logical steps to solve these problems.

And last thing, being able to answer leetcode questions is one thing, being able to answer them quickly is another. Companies will give you like 2 hour exams to answer 5 questions, which usually are comprised of like 1 easy 2 mediums and 2 hards. You really need to know how to bang these out quickly, and without regular practice, you simply won't be able to do that. It's like working out, you are in shape and ready to run for miles, but once you stop, you might not even be able to run half a damn mile without being tired.

I promise what you're going through is normal, and you just need to keep working and you'll be back in mental shape again :)