Increased Heart Beat. Had Heart Attack From Spontaneous Dissection Of Coronary Artery. Should I Be Concerned?

I am a 40 yr old female, had a heart attack at 37 caused by a spontaneous dissection of left descending coronary artery . Cardiologist thought may have been caused by migraine meds taken at time. Had two stents placed. Was on med regime including Coumadin and Plavix. Now down to Zocor, Coreg, low dose aspirin and fish oil for heart. Haven t been having any problems but woke at 6 am today with noticably racing heart - took heartrate was 126. That s 70% of my max THR. When I work out I shoot for around 135 or so, so that was disturbing. At rest I m normally around 90. Took a Coreg and eventually got down to in the 90s. Blood pressure tends toward the lower side usually. Should I be concerned about this episode? Don t remember any bad dreams or anything.