Vanishing twin?

Last week we went in and saw one baby measuring at 8w5d. After some joking my husband asked her to make sure there was definitely only one in there.

We found a second! Both had strong heartbeats but the second was tucked behind the first and she couldn’t get a measurement, she said it looked a bit smaller though.

We went back today (7 days later) and there’s no sign of the other one. No sac, nothing.

I’m feeling very empty and confused.

Is it possible it’s still in there? Has anyone had a vanishing twin come back?

We were shocked last week about the possibility of twins but really fell in love with it. Now I feel super empty.