It is normal for Anemones to expand and contract this is how they expel waste and exchange water in their column. I mainly notice this when I feed mine. After a large meal your Anemone may contract in the extreme and expel a slimy bolus (Anemone poo) I freaked the first time it happened I thought I killed it with food. One of the main signs of stress in this animal is movement if your Anemone is constantly on the move around the tank then it is not happy, but expanding and contracting is normal. If it roams check water quality first then light intensity (if yours needs strong light, some don't) changes in current direction or strength can also cause a major move.