Maybe for you tea is an allergen. Are you taking this - https://en.wikipedia.org/wiki/Salbutamol ?
bronchodilators and caffeine in tea are both stimulants and cause a rise in heart rate - when you combine them you may get even more of a response (called syngery) then you would see from either of them alone.
You could try drinking herbal teas that are caffeine free and this help stop that affect.