Welcome to HCM,
After going through your history,you have coronary artery
disease and heart attack
and treated with PTCA with stent
which is good as you are already on the road of recovery,I presume you must be taking all prescribed medicines.
is possibly due to prolonged rest or could be postural drop in BP just get checked your self for BP in supine and sitting and standing position if there is anything detected that is if your BP falls after standing then you need to see your cardiologist .
if nothing then just increase your level of physical activity and you will be all right.
Please take care of your diet and exercise and stress
Please take care.
Wish you speedy recovery and healthy life.