What kind of flow area is it in? I found that our leather is extremely moody, infact for the last 4 days it decided to tilt towards the back of the tank, only to find out that the powerhead that had been making a gentle current on it had fallen down slightly and so it had moved to where the current was, I also found that because I hadn't fed it like I normally have been it wasn't perking up. I'm not saying yours is like this, it could be shedding too, they do that also, they also act weird if something is rubbing it or touching it that it doesn't like. Personally I found that leathers tend to have a lot more personality than other corals.
Could be lighting too, I'm sure there are others a little more experienced than me but just thought I'd share with you what I've learned from our leather. Hope it perks up for you