Maybe it will come loose before you go to bed. Truthfully, people always say to cover the power heads with mesh and stuff like that, but I feel if the anemone is making it up there in the first place, something isn't right in the tank.
Whenever I add an anemone, they seem to squeeze themselves between the rocks, and then slowly come back out. They might move a few inches here and there getting an ideal position, but not inflate and blow around.
In the wild they do this to move to a completely different location.
You obviously can't leave the power head off all night if it's the only flow you have in the entire tank. Your fish would probably suffocate.