I am 3 weeks postpartum and have noticed that my heart is relatively fast during the day and dips down to the mid to upper 50s when I lay down in the evening. I am used to a slightly elevated HR because I have anxiety. Why am I experiencing the low heart rate in the evening since having my baby? I went to the ER for feeling lightheaded. My EKG was normal, my heart rate did not go below 74 while I was in the hospital and all my blood tests were normal (thyroid, BNP, electrolytes, etc). They found nothing wrong with my heart. Should I just assume this is normal? I am 28, slightly overweight, I have always had a low blood pressure, no known health problems.