Missed miscarriage after heartbeat -how common?

After a breather of not worrying, again out of the blue came the worry! I can’t take this!

I’m today 10+6 and went to an ultrasound on 9+3: everything was there, saw the heartbeat and doctor said that it looked like a very healthy pregnancy. Symptoms have come and gone but they exist (especially nausea and exhaustion).

Now I’m all of a sudden sleepless over:

what if something happened afterwards and I’m not aware? how possible that is?

next ultrasound is on 24th January so still exactly two weeks to wait.