My Jaguar (Managuense) cichlid's mouth got stuck open. She wasn't breathing much and after 5 minutes could not manage to get herself unstuck. Afraid she would die, I decided to catch her in the net and push her mouth back in with my finger. I have pictures of her with her mouth perma-open I'll upload if anyone wants to see.

It happened when I was cleaning the tank. She was attacking me extra hard. Serves her right! jk. She is fine now, back to normal.