You should always expect some variation in your CARS score, so don't freak out if you go up or down by a bit.
But if your score has been dropping significantly and you haven't changed your strategy recently, then the most likely problem is that you’re overthinking the questions.
...then you are probably overthinking the questions.
That might seem like a strange answer to you. Aren't you supposed to think carefully about the questions? Shouldn't you be thinking a lot about them?
Not necessarily. Let me explain why.
Unlike a lot of third party CARS (Princeton Review, Kaplan, etc.) the AAMC questions are mostly trying to test how well you can apply your knowledge of the passage in a simple, intuitive way.
To be clear, I’m not saying that their questions are easy. But even when they're hard, the correct reasoning is usually simple. So your first, gut instinct guess for a question is usually correct. When you overthink a question, that means you’re not trusting that gut instinct guess. Without even realizing it, you’ll often end up creating complicated arguments for why the correct answer is bad and the wrong answer is good. In other words, you’ll talk yourself into getting the question wrong.
To flesh this out more clearly, here's what happens when you overthink a question:
To fix this, you need to try to keep it simple. Try to avoid answers that you have to come up with a complicated argument to justify. Instead, listen to your gut instincts. If an answer sounds good to you, then trust that — it's probably right! Confidence is the key here.