Please help....

Anyone ever had one baby have a heartbeat and the other not at 7 week ultrasound or just an early one? The doc told me today that they didn't see a heartbeat on baby a. He said it could be vanishing twin syndrome or it could just be fine and we will see it next time! I don't get my next ultrasound until Monday so I have to wait all weekend to find out if I am still having twins or just one!! I am a wreck I don't even kniw how to feel