1. Caffeine from coffee, tea, soft drinks, energy drinks! or -- stress
, lack of sleep.
2. medications - decongestants! , antidepressants, and many others cause fast heart rate
3. Cardiac conduction problem, such as Wolf parkinson
White Syndrome, or another conduction abnormality.
(can happen even in young people).
Cardiac infection or tumor (we are talking more serious here, but very unlikely).
GO AND SEE YOUR DOCTOR, insist on EKG and you also need a cardiac consult.