It's most likely already dead.
Its Dieing .
Your Goldfish probably has a problem with its swim bladder. It's may be what the goldfish is being fed that is causing the problem. There is not normally enough fibre in the food we feed our Goldfish. This can lead to constipation and pressure on the swimbladder, which is the organ that keeps the fish buoyant and upright. The fish floats upside down because of the pressure on the swim bladder. Frozen peas are the answer. Defrost them. Take off the outer skin and then crush the peas. Feed them to the goldfish. It may also help the goldfish to put it into a container with shallow water in it - use water from the fish tank. Feed it the peas. Hopefully you will see an improvement in a very short space of time.
Goldfish die in cold water because they are not used to the water tempurture. But if you put the fish in a bag and set the bagin the cold water the water in the bag and in the tank will be come the same tempurture.
Upside down, its an awesome hot box.
It is possible, but the goldfish might not want to eat. It's injured, and it's trying to rest. It depends how bad the injury is too.
I'm not sure, but, I had 2 gold fish die recently for no apparent reason. Am wondering if the upside down cat fish hurt them in any way. He always chases them around & they act frightened by the cat fish.
Yes
If your fishes dorsoul(back fin) is down it usually means that your fish is sick. Most fish can live up to 3 months when sick. But some even longer. It all basically depends on what type of illness it has. In some cases it could be deppresion.
Gold fish will swim upside down if they have a swim bladder infection, try feeding it fish food that sinks because, when it eats food at the top of the tank it swallows air that goes to it's swim bladder causing it to go upside down at the top or bottom of the tank. Hope I Helped :)
It is important to remember to put things in a goldfish tank, even goldfish get bored. Some of my suggestions for tank decor are artificial plants and a "hidey hole" for your goldfish.
You should not have goldfish and platies in the same tank ever.
Well it actually means nothing