It could have got hurt by The Rock. It could have been stuck under the Rock did any? Do you know of anything stung it another anemone or anything? If you have aptasia under the rock it could sting the anemone but that's not really normal I would just wait to feed it for a couple days. To repair itself a little bit and then just feed it some food. It should be okay if you have like vitamins like a doser. You could put a little bit of vitamins in the water so it can help it repair but it should be okay if you don't just feed it. Let it do its thing and it sure repair this will happen to mine. Half of it got stuck in the blower and half of it was gone. It was a long tentacles and then it repaired itself In a couple of months but this doesn't seem that severe