Yes, it sounds like Swimbladder unfortuantly.
You can treat it, but you need to find out what is causing it first. Some things that can cause swimbladder are...
Constipation - Constipation is the number one cause of Swim Bladder Disorder in otherwise healthy fish. I'd try treating for this first, before using antibiotics or anything. Try feeding a pea, or just not feeding for a few days.
Overfeeding - Does he display signs immediately after feedings? And the symptoms tend to go away after a few hours? If so, you are probably overfeeding. It is helpful to remember that Platies only have stomachs approximately the size of one eye, so try to feed smaller meals several times a day.
Injury - Sometimes fish who have recently been through a traumatic experience (being dropped on the floor, being in a fight, etc) may display Swim Bladder Disorder symptoms. In these cases, many times there is permanent damage to the swim bladder. Unfortunately this means that there is no real cure for the disorder if it is caused by injury, but you can manage the illness.
Bacterial Infections - I've never seen a case caused by this, but I've read some other people have. So I can't say much about this.
Any thoughts on possible cause?
