feeling sudden heart jumping in center of chest only for few seconds like 3 to 6 second , occurs at any time and minimum 1 episode in between 1 to 3 month , fear occur at that time. small fatigue also occur. ECG , EcoCG, EEG, Ions, CBC, BP, DC, Thyroid are normal . No family history of heart problems. Still it is undiagnosed. when ever it occur, i try to understand it, but due to insufficient of time of occurrence, i can't able to understand it. what is it ? Also i do regular exercise. and it occurs from 2 years and my age is 21. my height is 170 cm and weight is 50 kg.