It probably means the fish is badly damaged and is dying. Please do a water change ASAP. Bad water is the commonest cause of death in goldfish. In order to keep fish sucessfully there are a few basic rules one MUST observe. They are :- 1 inch of fish needs at least 1 gallon of water. Every tank must have a permanently running 'cycled' filter. :- Every tank must have at least 50% of its water replaced every week..
if it is not swimming and it lays on its side then it is dead.
Swim bladder disease? http://www.straightdope.com/columns/read/1688/if-a-goldfish-is-swimming-on-its-side-is-this-a-bad-sign
No!
Cause They Like Swimming Side Ways
If the goldfish is swimming in water, it is alive.
When their swimming upside down its usually a sign that their dying
it stops swimming
Yes
Yes. It may have a hard time swimming for awhile until it gets used to it. Sorry, there is no cure.
Gravity
If goldfish are constantly swimming, it may indicate that they are stressed, bored, or lacking adequate environmental enrichment. In a well-maintained aquarium with enough space, hiding spots, and social interaction, goldfish should exhibit a more relaxed swimming pattern. Constant swimming can also signal that the fish are trying to escape poor water quality or high ammonia levels. Monitoring their environment and ensuring proper care can help reduce this behavior.
Because your goldfish is dead.