Physical Emotions

What does it mean when emotions are so intense it becomes physical pain? What is going on inside?

When you are sad or in pain, tears would not seem out of place. Neither would they be too out of place if you were overcome with joy; or shock even. A laugh or excited dance would perfectly complement a person's happiness. These things, I can understand.

But …what is it when you are missing someone so badly, your chest (your heart?) feels as though it is shrinking and becoming tighter and tighter to the point you gasp for air; whether in shock or because your lungs forget how to work for a second, I don't know.
Does anyone know what I'm talking about?

…Maybe I just need to go to see a doctor. :S.