I got a few Angel fish a couple of months ago, they seem to be fine, however one displays a weird behaviour. Firstly he would be isolated for periods of time staying on his own in very close to the back glass and behind an electrical cable (how he manages to fit there). Whereas his mates swim around normally. Then he has started pointing upwards, at any depth, first it was a small pitch up, but recently it is much more pronounced, Today he was almost vertical. When I feed the fish he eats. Is this fish dieing?