I have been having heart palpitations off and on for a couple of weeks. I think it may be my synthroid medicine for hypothyroidism. I also have had off and on intermittent ache/burning pain under and lateral left breast along with off and on dizziness. I don t take bp meds but my ob/gyn said that my bp was 144/96 last visit a couple of days ago and recommended diuretic. My internist says no I don t need bp meds don t normally have bp issues. Today it s 109 outside locked my keys in my car. Out in the heat for about 1hr trying to get car open. Came home literally walked in from car and my heart started beating so fast and hard I thought it was going to explode. Totally scared me. I don t know if this is anxiety or heart issue. I m 46 yr old female going through the beginning years of menopause.