Probably got constapated and has swim bladder issues. I don't know that much on this, but I think you can fast him for a day or 2, then feed him part of a shucked pea to aid digestion. If possible, get your water tested as bad water quality doesn't help. Water changes don't hurt a bit, so I suggest to do some partial water changes over the next few days to reduce stress.
gravity
buoyancy
upthrust
gravity?
The same thing that keeps you from floating out into space. Gravity.
the density
Gravity.
The answer is an umbilical cord. It keeps astronauts from floating out into the universe.
The force of the Sun's gravity keeps them in their orbits.
Buoyancy
gravity?
what keeps the moon from flying off into outer space