The words "just calm down" does tend to help the OTHER person who is not suffering from anxiety or a panic attack. But if you do suffer from anxiety watch the video below for 10 ways to deal with anxiety.
Don't follow the perception other people have of a situation, give it your own meaning.
2. Anchoring
Use physical, vocal, or music triggers. Remember how Tim Taylor from Home Improvement used to grunt? That is good exercise in controlling your emotions. You don't have to grunt, but find something else that helps you control your emotional state.
3. Speak Well Of Yourself To Yourself
4. Be Healthy
Healthy Mind, Healthy Body, Healthy Soul
5. Practice Being Calm and Relaxed in Challenging Physical Situations