Vaginal bleeding ?

Abigail • First time Mom of Baby Girl Alexandra my Christmas baby 12-25-19 👶 🌈

So earlier this week hubby and I finished moving. At around 2AM I felt some really heavy discharge and when I wiped I saw dark red blood. I quickly told my husband and we went to the ER. There they ran some blood test and an ultrasound confirmed that baby was fine with a heart beat at 165. I guess my question is has that happened to anyone else ? And does the heartbeat seem like a strong number ? .. they diagnosed me with a threatened miscarriage but they don’t really know what caused the bleeding since my cervix was also closed.