Psychological projection...

Neurotransmitters, which are the body's messengers, start firing off. Okay, that's as much biochemistry as my mind can handle right now.

"Robert Emery and Jim Coan, professors of psychology at the University of Virginia, explain in Scientific American that it could be down to the anterior cingulate cortex, a region in the brain thought to regulate emotional reactions. They suggest that the anterior cingulate cortex becomes more active during stressful situations. This region is thought to stimulate the vagus nerve, which starts in the brain stem and connects to the chest and abdomen. This stimulation is thought to lead to the 'pain' we feel in our chest."