Thank you for your query. It is remarkable that you have picked up on your symptoms and thought of seeking help even though you feel better. Atrial fibrillation can have a slow rate ( common when under medications) or at rest, or a fast rate. The fact that you had the tachycardia( fast heart rate) , enough to cause you discomfort and apprehension, while on medications, is reason enough to visit your physician/ cardiologist. your medicines may need to altered or your physical activity controlled. This is best advices after examining your overall fitness which includes the fitness of the heart. if you have a persistent AF( atrial fibrillation), correctable causes should be treated. I recommend you see your doctor at the earliest and in the meantime, go easy with the exercising and don t do anything that increases your heart rate or strains your heart too much. If you have giddiness, breathing difficulty, palpitation/ racing heart even on rest, chest pain, unexplained profuse sweating, please visit the ER right away. Hope this helps. please get back to us if you have further queries. wish you good health