For those unaware, sea anemones attach to rocks and other solid surfaces via a “foot”, like a snail’s foot. They can crawl, very slowly, if the situation isn’t to their liking.
My guess is this one crawled over the powerhead and got pushed away from the wall, and is now unable to react fast enough to grab onto something. I’m sure it’ll eventually land and grab on, but for now it’s gonna float around some.
It’ll be fine. They’re photosynthetic anyway, and the fact that its tentacles are all extended means it isn’t overly stressed.