Often, when you have been doing a considerable amount of practice, you suddenly feel like you’re getting much WORSE instead of better.

In my experience, this is actually a good thing. You aren’t getting worse. It’s just that your ears are now more acutely aware of the things about your playing that could be improved. You’re developing a more critical perspective.

Keep plowing through. You’ll get over the hurdle. Sometimes a little self-awareness is uncomfortable, but it means that you’re improving.