scariest 5 hours of my life

Tonight at 13w1d, I started bleeding. Heavy! Like it was pouring into the toilet making the water red. Rushed to the ER. Thank goodness I work at the hospital and thanks to my boss I was in and seen within the hour, scanned at one and a half hours in. My babies hearts are still beating. My twins were even having a dance party. No placental tears. No blood behind the placentas. No blood around the babies. Amniotic fluid was normal. I'm home now and luckily I have an appointment with my high risk OB on Friday. So I'm staying in bed until then. While I'm happy with the information given, im still concerned. Where is this blood coming from?! It's accompanied with light cramping. I'm keeping positive but I'm a "I need  a logical explanation" kind of girl. Anyone experience this?! I hope someone has words of wisdom for this first time momma!