Hello and thank you for using HCM.I carefully read your question and I understand your concern. I will try to explain and give you my opinion. A person that previously had a heart attack means that suffers from coronary artery disease and of course has a biger risk than the other population to do problems again. This category of patient might feel tired, lethargic for different reasons depending on heart function, blood pressure, cardiac frequency ect. For example a low cardiac function might be responsible for difficulty in breathing deeply, decreased physic tolerance, lethargy. Feeling sleepy might be a side effect of medications. Feeling tired, nausea might happen even from other patologyes like thyrood gland problems. So, I encourage you to help your friend and convince her to meet the doctor becouse it might be something treatable and she will feell better. If I was the treating doctor I will recommend some examination like an electrocardiogram, a cardiac echo to evaluate heart function, a full blood analyze to exclude anemia, hyperthyroidism or electrolyte imbalance. After this we can better understand what is the problem and menage it. Hope I was helpful.Wish your friend good health. Best regards.