Why is it that when i get sad i have actual physical pain in my chest?

Sad or depressed?: Sadness can cause shallow breathing & chest tightness, leading to discomfort. Depression is assoc'd w/ low serotonin (5ht). 5ht has pain gait-keeping functions & helps keep blood vessels flexible, low 5ht may increase pain, cause poor sleep & migraine headaches. Some antidepressants, such as Effexor (venlafaxine) and elavil, which increase 5ht and norepinephrine, are used treat some pain disorders.