Anxiety disorder is one possibility, but before considered we should always rule out any cardiac problems. The sensation of feeling ones heart beat is called as palpitations, which can arise due conduction problem in the heart. This palpitations start suddenly and may resolve to normal rhythm on it own. ECG cannot diagnose this problem.
If cardiac work up is normal then anxiety disorder and night terrors could be the possibility which can be easily treated by a clinical psychologist by psychotherapy.
Next Steps
Kindly meet a cardiologist with specialisation in electrophysiology, he may ask you to get a test called holter monitoring which has higher chances to catch the palpitations and by seeing the type of palpitations they can provide you specific treatment.
Health Tips
Until cardiac workup is not done avoid any intense physical activity. And in case of such palpitations go to the nearest emergency and take an ecg at the time of event.