From what I can see it's dying [emoji20]
When the foot and tentacles just "deflate" like that it's serious trouble. When the body envelopes the tentacles that's a normal defense or even feeding. Keep a very close eye on it and if you start to see any decay remove it from the tank immediately.
Now the tentacles have reinflated, but the base is still deflated. If a clownfish can save an anemone, this one is surely trying.... Here's what it looks like now:
It may have just spawned prior to the picture you took. They can get very deflated thereafter. It looked better in that image you posted as a followup. Can you post up all your water parameters and how long the lights are on daily (as well as what type), please?
The base just keeps getting longer and longer. It's spread to 4-5" across and getting thinner. The tentacles keep inflating and deflating. I think it's splitting!