Hi M.,
It can be scary...of course it can. Anything that goes "wrong" during a pregnancy is scary, because you worry about that beautiful life you're keeping safe.
I too was diagnosed with PP at about 20 weeks. At 30 weeks I had heavy bleeding, and it was determined that I had a placental abruption, where the placenta actually tears. I was in the hospital for a week, monitored constantly, then sent home on bed rest. Had to call the school where I was teaching and tell them I wouldn't be back in, not even to pack up my books. Very scary.
But, and here's the wonderful part...the day after his official due date, at a glorious 40 weeks, one day old, I delivered my son, vaginally and quickly (only 4 hours of labor!). He was a healthy 8 pounds 7 ounces, 21 inches long.
As many others suggested...do whatever your doctor suggests. Rest more than you feel you should and try not to worry. As long as you feel that little one kicking and rolling, know that s/he is doing well.
My wishes for an easy, worry-free remainder of your pregnancy, and a smooth labor and delivery.
T.