Hello and thank you for using HCM.I carefully read your question and I understand your concern.You shoud not worry .I ll try to explain you something and give you my opinion . This fllutering sensation might have to do with a rhythm issue. There are some electrical impulses that generates from different parts of the heart different from normal sinus rhythm.They cause a premature heart contaction or chaotic rhythm and you experience this symptoms like palpitation, flattering sensation, anxiety, difficulties in breathing deeply. This are sporadic episodes end of course doctors can not find them in you are not monitored in that exact moment.The doctor can see in if you are monitored in that exact moment. If this happens once a wile you should not worry. If they persist you should do some examinations like a fool blood analyze to exclude anemia , hyperthyroidism that sometimes couse this rhythm problems. Than a cardiac echo to evaluate heart function and valves and the most important one holter rhythm monitoring. This is an apparat that monitor your heart rhythm for 24-48 h.You can repeat it once a wile to rise the possibility to chek anything. Mean wile avoid caffeine products and energy drinks becouse they exacerbate your symptoms. Hope I was helpfull. Best regards.