I understand your concerns. Sudden onset chest pains, palpitations, fatigue
and breathlessness are very likely to be the manifestations of psychological stress
or physical overwork. This is especially a possibility since all your tests have come normal.
I would suggest a tranquilizer as well as an antacid
(since stress does cause acidity and reflux), look in to probable stressful factor in your life and address it.
, especially acute thyroiditis
can present with similar symptoms. It is worth doing T3, T4, TSH levels on blood.
Dissection of aorta is another rare possibility but this can usually be picked up by clinical examination and a 2D echo