Your anemone, M. doreensis, is a sand anemone. Don't try to put him on rock - he will only be happy in the sand. As people have pointed out, any anemone, when placed in a new environment, will go through a period of acclimatization, during which they will inflate and deflate to balance water chemistry and remove waste.
Can you take a pic of the anemone in the current condition? Additionally, if your anemone dies, it will normally take a little time (12 hours or so) to start decomposing, so it is rare to have a single anemone death crash a tank unless you leave the body in there for several days.