My goldfish has been doing the exact same thing! She has been very quiet, lying still for weeks (after being a very active and friendly fish for the 6 months I've had her). Now she is swimming around but strangely. She swims with her head up and tail down. In addition she swims backwards (she swallows water excessively until she floats backwards almost as if she's skydiving out a plane backwards). She is also barely eating, and food used to be her sole joy in life. I thought she may be pregnant again as the last time she lay still for weeks she was making eggs, but this time her stomach isn't bloated and I'm not seeing eggs. Did you ever figure out what was wrong with your baby?