I discovered this month that Google returns 951 hits when searching the phrase "I swallowed my crown".
Now that I have had that not-so-singular experience, I figured I should make it 952.
O.K. Google - start crawling.
P.S. It's nothing to worry about - it will pass. Your dentist may want you to retrieve it - to use it as a reference to make a new tooth - which will save time. It's really up to you. If you find it, I would advise boiling it - you KNOW where it's been!