I guess the relevant question is, "Do they right themselves during the day, or do they have trouble remaining horizontal?" If the latter is true, you have a problem. If the former is true, then yes, I have had fancy goldfish who seem to go nose down at night and are normal during the day. I have even had one that "reposes" on her back in the plants, then gets up in the morning to feed and acts completely normal during the day. They're weird little critters.