Hello there and thank you for using HCM. I carefully read your question and I totally understand your concern. Don t worry, I will try to explain you something and give you some advises. As you describe, my opinion is that we are dealing probably with a heart rhythm issue. It is difficult to tell what is exactly. You may feel that your heart is racing whith frequent beats for different reasons. It may be a simple tachycardia. It means that your heart beats exceeds 100 beat for minute. It may happen for many reasons to simple emotional stress to different pathologist. There may be a different rhythm problem.If your heart is beating too fast and in a chaotic way, not rhythmic, it may be what we call atrial fibrillation. This may cause you palpitations and breathing difficulties. If you feel like skipping a beat, it may be an ekstrasystol. So, if I was your treating doctor I will recommend you some simple examinations. As you have done all the others I will recommend a holter monitoring to register and see what happens with your rhythm during the night. If you feel that your heart is beating in a chaotic way. it is advisable to make an electrocardiogram in that exact moment to your nearest cardiologist. In mean time avoid coffee and caffeine products because they exacerbate this symptoms. When we document and see what kind of a rhythm problem is this we can talc about treatment. Hope I was helpful. Wish you good health. Best Regards