As said by you ..you get these palpitations some time..not having any particular time or precipitating factors .every time your ecg shows sinus rhythm . Now have ever your ecg done when you are symptomatic . That is when you had these flutter like feeling . This is important . If not you need continuous monitoring of your heart activity that is continuous ecg..We call it Holter monitoring . This will record your ecg for 24 to 48 hrs as is the suspension or requirements . This is a small machine you can keep this in your pocket and can do all his work.this will show any abnormal rhythm if any..apart from this get your sugar ,thyroid and hemoglobin level checked.hope this will help.