Hi, The causes for your symptoms could be several and some of them are as follows: anemia, vitamin and mineral deficiency, protein deficiency, the increased circulatory volume during the mid-trimester of pregnancy leading to a state of increased work load on the heart pump and thus causing arrhythmia, decreased vascular supply to the upper part of the body perhaps due to pressure effects and so on. A proper assessment by a physician should be able to detect the exact cause and plan further management. Please take adequate rest preferably in the left lateral position, eat a healthy diet and avoid stress. Wish you safe motherhood.