my goldfish is swimming backwards,upside down and sideways...do they feel pain
The pain thing is sort of debated, but for the most part yes fish feel pain.
Chances are your fish was improperly acclimated or if your tank is new it is going through a process called cycling which put your fish in this condition. I would let the fish naturally die in the tank though if it is going to die. The most common ways of disposing of fish are much less humane than letting what will happen happen. There is a small chance it will recover. It is weak and caught in the current of your tank.
What size tank is it? What are your water parameters (levels of ammonia, nitrite, nitrate, & ph)? Is the tank cycled? I would do a 50% water change asap with temperature-matched, properly conditioned water. It sounds like your fish is suffering from his water conditions. Yes, i do believe fish feel pain- any creature with a nervous system is capable of responding to nerve stimulus in a negative way. If you feel your fish is suffering unduly, you should consider your options carefully- humane euthansia is one of these options rather than letting the fish suffer a horrible demise. I would try a water change first & see if he shows any improvement.
Not sure but it might be swimbladder disease
Its cuz of too much air inhalation
Try feeding it deshalled microwaved peas
Even if its not swimbladder its still good prevention against swimbladder