My post above was intended to give hope of an easy remedy to your worries.
I have been interested in chemicals affecting heart rate for a long time. I am now more than interested in minute traces of chemicals causing anaphylaxis. I hasten to add that this is only an example of how we can be affected by such small amounts of chemical interference.
Many years ago several pilots lost their medicals after failing an ECG. In most cases the need for the ECG was dictated by their AME after finding symptoms not dissimilar to yours and a clear anomaly was found at headquarters. (It was some years before AMEs had their own ECG machines.)
Some time later I was surprised to hear that coffee was blamed for the problem. No coffee, no symptoms. Gallons of boredom relieving brew on the flight-deck, a raised heart beat and a modified ECG readout. Not surprisingly the pilots wanted the livelihood back.