Hello and thank you for you for using HCM. I carefully read your question and understand your concern. I will try to explain you something and give you some advises. Someone might experience fast and hard heart beats for different reasons. The simplest one is sinus tachycardia. This means that your heart is beating over 100 beat for minute. Its normal range in resting situations is between 60-100 beat for minute. Sinus tachycardia might happen for different reasons from simple emotional stress to different pathologist like anemia, hyperthyroidism and of course from excessive consumption of caffeine products. You might have not experience such high frequencies before but long time excessive consumption of caffeine product of course lead to sinus tachycardia. Having high frequencies when you train is quite normal. We expect your heart rate to be high up to 220 minus your age, but this is not quite normal during resting states, before sleep. Sinus tachycardia might give this pounding sensation, an anxiety feeling and difficulties in breathing deeply. So, if i was your treating doctor i will recommend you to stop caffeine supplements. You might feel much more relived. Than wait and see what happen. I encourage you to continue training because it helps the heart to adapt and low its frequencies. Hope I was helpful. Best regards.