I don't think emotions act like this, ( if don't freak out now then on the exam ) .
I think its good to be cool and confident.
cuz that will have a good impact on your mood and performance
don't say to yourself that you should be freaking out cuz then you will
and believe me you don't need to have a panic attack, this will affect your judgment and performance and subsequently bad marks will result.
Be Confident and you CAN DO IT
Good Luck