Sounds like its just releasing waste and getting use to your tank. Anemones do this often, they deflate to get rid of waste. They will do it for hours, some times all night and even durring the day. I found this website that shows you pictures of what an anemone looks like when it is deflated, getting rid of waste, and also what they look like when they are dying. Do a search on google for karens rose anemones. I can't give you the link because they don't allow us to post websites on this forum. It will really help you understand your rose anemone better.
