"Just calm down" are three words that never has the desired effect.
This happens: The opposite. The person becomes more activated. We all know this: That when you are worked up, calming down takes an unreasonable amount of effort.
So let's go with where the energy is at. If I am worked up, could I also calm up?
"Just calm up!"
This can be done. Acknowledge the activation, and meet yourself calmly where you are at.