It will go back to its normal size in a day or so most likely. When anemones are "stressed" they just get up and walk around the tank until they find a spot they are not stressed in. Worst thing a person can do to an anemone though it to keep moving it by hand just to put it in a place you want it to be. Anemones will always move to the place they like best, not necessarily the place you like best. Also, when anemones "digest" they shrink up so small you may think it disappeared because it is behind a rock. That is normal as well.