Now the fear really sets in. You know you'll be asked questions about your Jewish lifestyle and knowledge, and you know that you know a lot. Your local rabbi knows you know a lot or he wouldn't be approving you for this next step. It feels like, for the first time, everyone is behind you and wants you to succeed.
This is when your mind will become your own worst enemy. You become convinced that you're not ready, you're going to fail yourself and your rabbi, and you'll set your conversion back years.
...Or maybe that's just how I think.
Anecdotally, people consistently mention a similar fear of "messing up" questions. Here's the secret everyone messes up something. Inevitably, it is something inconsequential and something you know as well as the back of your hand. Normally, each person remembers one specific "duhhhhr" moment, but there's no limit to how much nervousness can derail you.
So now that I've convinced you you're going to screw up in their beit din meeting, let me reassure you. Don't worry, these feelings are normal. I'd be more worried if you felt like you passed with flying colors.
We're human; we get nervous. Rabbis are also human, and they see enough conversion candidates to know that some flub-ups are normal. What they look for is how you flub up. Your body language gives away a lot of information when you have an answer on the tip of your tongue. On the other hand, if you give a wrong answer cooly and calmly, that tells the rabbis something very different. If you look clueless, it probably means you didn't even see the question being asked.
The information a rabbi can collect from your mistakes is invaluable. And it's generally for your well-being (it should always be for your well-being, but we know better that there are mean and/or incompetent rabbis in this world). The idea behind a halachic questioning is to probe your knowledge until you run out of information. They keep asking questions on a topic until they reach the limits of your knowledge. That's an excellent way to get a rough estimate of your strengths and weaknesses.
So don't fear the question you don't know, whether you honestly don't know or whether it's on the tip of your tongue. It's really not a big deal at the end of the day, no matter how crushing it may feel at the time.
Take a deep breathe. Relax. You'll laugh about this later. (And if you're like me, you'll completely forget what it was about! I guess I could search the blog to figure it out, but nah...retroactive ignorance is bliss.)