Hi, Fast heartbeat and feeling panicked can be because of various reasons ranging from simple anxiety or stress to simple or complex arrhythmias (these are abnormal heart rate and rhythm). Also, hyperthyroidism which is excess of thyroid hormones, overuse of certain substances like alcohol, coffee, tobacco can precipitate these kind of symptoms. If you were my patient I would have ruled out some rare heart related conditions like cardiac arrhythmia by doing Electrocardiogram (ECG) and thyroid disease by ordering thyroid function tests. Please follow up with your doctor and also manage stress appropriately. Take care!