Mine does it all the time every couple days, most of the time it expells waste, sometimes not, but seems normal, sometimes mine will get even smaller than that and look kinda pathetic, but in a couple hours will open back up and look great.
It will also move around and eventualy pic a spot to stay, or at least thats what mine did. It moved around the tank for about a week and picked a spot on some live rock and has stayed there every since (about 6weeks now)