DrDonna shall I tell you not to worry and get a grip?? Will you listen?? 
I realised the other day that although I have seen a HB and still feel pregnant (although not many symptoms - nipples like bullets, waves of nausea, tiredness) I can't seem to reconcile in my head that everything could be ok. I keep expecting something to go wrong, I think its because at this stage I am remembering my miscarriage and my ectopic pregnancies and not my 2 successful ones.
So I think all this worry is normal and there is nothing we can do to control this so just roll with it! And if you're anything like me, keep a countdown chart in your head until your next scan. Mines on the 14th as we're off on holiday on the 18th (long distance for 10 days) and I wanted some reassurance.