Low placenta

Okay so yesterday I was at work and fell down the stairs and landed on my back so I obediently went to the Er they did test everything came back okay she was hyper heart beat was good no bleeding . But they said my placenta is low . I’m 15 weeks and she said it should move as the baby gets bigger but I’m nervous so I have to call my OB tomorrow for an appointment. I was wondering has anyone experienced this and should I be scared or how was your experience with it