Usualy swim bladder would cause this sort of thing but swim bladder can also be caused by a variety of things itself - including the wrong kind of food and internal bacterial infections.
Internal bacteria infection. I'm pretty sure that's what it is. I just hate looking at this sick fish I need to take a break from fish keeping and plan accordingly for my new tank after I've read all of the helpful cycling facts and facts from this forum! I'm re reading everything. I feel terrible for not choosing wisely lol and now I have caused the almost death of this neon tetra. It may just be another fish, but for me its heart breaking!
treat with an anti-internal bacteria med/antibiotics in the food and feed a shelled pea too.
If you want links to some other helpful articles, there are some in my signature. Don't give up on fishkeeping
Everyone makes mistakes and with a little research I'm sure you could start a-new and do very very well with it.