Honestly, it looks dead/dying to me. You can see a lot of recession there exposing the skeleton (you shouldn't be able to see those white ridges). Brown jelly disease looks like that - the polyps melt into a brown goo. If you have any other corals in there I'd remove it and put it into quarantine as brown jelly is contagious.
Sorry, should've been more specific.... were looking at the long brown tendrils that are coming from it, i initially thought they were some kind of long tentacle that i read they use for defend their space from other corals getting too close, but they detached after several minutes.
You still shouldn't be able to see that ridges like that even when it's "asleep". And I'm aware you were talking about the brown tendrils - as was I. What you are referring to are "sweeper tentacles that search for food and they should look like normal ones just longer and thinner. I still believe the brown you are seeing is decomp/disease...
Wow, I'm surprised it opened that much. I'd never have guessed from the previous pics. I'm still worried about the exposed skeleton - mine sleeping look about like yours open. It does look a little pale to me though - you haven't noticed any color loss since you got it?