This looks more like a cynarina species (donut coral, meat coral etc) than an open brain. It looks like it's in a partial state of inflation or deflation. It should either completly inflate or deflate in the coming hours.
Agreed if have you performed a water change or made any changes to the water? these types of coral will frequently inflate/deflate as scott mentioned to adjust to water parameters
i've seen it inflate and deflate but the bulges are there most of the time ... it fell into the sand during a minor rock slide while i was on vacation 8 months ago ... when i found it part of the fleash had died in that area ... but it came back ... maybe scar its tissue???