Bleeding at 23 weeks

I'm 23 weeks pregnant and this morning I woke up with a fair amount of vaginal bleeding. It was bright red in color so it was fresh, like a heavy period.  I went to the doctor and he sent me to get another ultrasound. Everything checked out fine and they couldn't find anything wrong. They think maybe I could have popped a blood vessel on my cervix but they really don't know. Has anyone experienced anything like this before? Of course it made me extremely nervous.