Hi Geoff,
Unfortunately, if you click on the link to review a guest, but didn't complete it, it goes away (has happened to me many times). To get it back, go to the email you received in your real email (i.e. not the mail built into the site) and click on the link. You should also be able to get to the review page, by going into your own profile on the site and then clicking reviews and then reviews by you.
If you haven't received any notification (either in your dashboard or via real email) then just hang tight, sometimes the review emails are delayed by about 24 hours.