Ok, obviously you DO need help if your fish is sideways! This is really bad. Do some partial water changes and check everything! check ph balance, nitrates and nitrites, ammonia...I'd recomend buying a water quality test kit for these. Check the filter, heater and the temperature. If everything is okay and you can't find anything wrong, I'd assume that he has a swim bladder problem or other disease. Talk to a pet store person and see what they have to say. I'd ask them what kind of meds to pick up for him while you are there.
