No, it's not dieing. Sometimes they'll puff up like that when they're hungry. This increases the surface area and makes it easier for the the coral to catch something out of the water column.
Inflating like that also helps them move. A strong current would be able to move the coral a few inches much more easily when it's inflated, as opposed to the second picture where it's more of a solitary rock low to the ground. The sails have been raised so to say. GL.