It seems like for you preparation is even more important than usual. It is understandable to not be comfortable under an artificially created pressure situation

It seems like for you preparation is even more important than usual. It is understandable to not be comfortable under an artificially created pressure situation (such as in an interview room). In that case, you need to prepare at least 3 times harder beforehand. First, research (online and offline) about all possible questions that they may ask. Having an idea about their codes and what they're doing will help with this. Then, prepare answer for these questions and rehearse them until you get sick of it. Take a break, come back, and rehearse again till sickness. Repeat.