As someone gets into better shape, their resting heart rate will become slower. I am certainly not a doctor, but 37-39 seems abnormally low.

Did you lose a lot of weight in the past eight months ....Do you have super low blood pressure now as well? I would be concerned if I noticed such a drastic change in such a short period of time especially if I felt tired or became dizzy at all.

Only you know what your medical history is and what changes your body has undergone as well as what kind of drastic measures you have put yourself through to reach your new fitness level. If you have any concerns, perhaps you should give your doctor a ring and see what he/she thinks. A doctor would be better qualified to evaluate your heart health.