6 weeks and bleeding like AF!

Yesterday I turned 6 weeks and this is my first pregnancy. Around 7:30 am I had bad cramping like my chums are on it's way. A couple of minutes later, I started bleeding heavily. I lost all my hopes. I was rushed to the hospital. A transvaginal ultrasound was done and for the first time could hear my baby's heartbeat. I was all numb. As soon I heard the heartbeat, I bursted in tears. I am glad that my baby is safe. Then where did the blood come from? There was bleeding in my utherus like a hemorrhage. I pray that no mom-to-be should ever experience this but has anyone ever experienced anything similar?