Did you feed the tank recently? If so, both haddoni and gigs open their mouths like yours is doing in the photo when food lands on them. In your case though, I lean towards an internal infection because the tentacles appear extremely tight and it looks partially deflated.
Keep in mind that you will need to act quickly in order to save it. IME haddoni go down hill a lot quicker than other nems such as gigantea. Once you can see physical characteristics of an ailment (deflating, lose mouth), you only have a day or two before attempting to treat it or it won't work. (again, this is IME with two different red haddoni, which never responded to treatment -- gigs I've treated responded right away).
Definitely begin Cipro treatment ASAP.