Yup, they can become detached for a variety of reasons, and rarely can you put an anemone where you want it (or where you think it would want to be). It is best just to let them figure out where to go.
The trick with anemones is usually to give them a bit more time unless they smell, are really just an amorphous pile of goo, or your water quality is clearly showing that something is dead. Otherwise, they can look terrible to us and then become perked up again.