We have two upside-down catfish that were normally very active around the tank, now they've buried themselves into an Anubis plant and will hardly ever come out. They look pretty skinny and a bit paler. We think they're a male and a female, but we're not sure. Any ideas on what's wrong? Are they sick? Are they preparing a nest? So far we can't find any information about this on the internet or our catfish books. Anyone got any idea on what's going on? Please and thank you all in advance!