there are many causes of palpitations.
the most common pathological causes are anxiety,thyrotoxicosis,anemia,valvular & structural heart disease
,sick sinus syndrome
if palpitation is associated with sudden loss of consciousness
for a brief period,dizziness then a cardiac conduction problem is most likely.
it may be periodic.
in that case an ECG may be normal.
ecg abnormality only obtained during palpitation.
so a continuous ecg monitoring(holter) may be helpful.
it is better to consult a cardiologist