<s>[INST] Im a 20 year old female and have a 23month old daughter. height - 172cm, weight - 68kg. A few months ago i noticed my heart was randomly beating fast for a couple seconds. It doesnt hurt and i can breathe fine,I notice it mainly when Im lying down or when im relaxed.  It happens a few times a day. medical history - Ive been taking Mirtazapine 30mg tablets for about 8months to help with my mood and sleep. My father has high blood pressure and my mother has MS. Ive never had any problems with my heart or any other serious illness. I am just a little concern and want to know if it is normal. [/INST] Hello! Thank you for asking on Chat Doctor! I carefully passed through your question and would explain that your symptoms seem to be related to anxiety. Nevertheless, if these problems persist, I would recommend consulting with your attending physician for a careful physical exam and some tests to exclude possible cardiac arrhythmia or any metabolic causes: - a chest X-ray study- an ambulatory 24-48 hours ECG monitoring to examine your heart rhythm trends through the day-complete blood count for anemia-thyroid hormone levels for possible dysfunction- blood electrolytes for possible imbalance. If all the above tests result normal, there is nothing to worry about. Hope to have been helpful! Wishing all the best,  </s>