Wow, he looks really pale, too
. Is his coloration really like that? You said it was normal but it seems paler then it should be.
As much as I hate to say it, he might have Neon Tetra Disease
Symptoms include restlessness, pale coloration, a "lumpy" body, difficulty swimming, a curved spine (at advanced stages), and bloating/secondary infections like fin rot. Infected fish will often stop schooling with the others and swim strangely.
It's caused by Pleistophora hyphessobryconis
, parasitic spores. Neon tetras are usually infected when they eat or pick at a dead fish or eat live food with the disease.
There isn't a known cure yet and the fish is usually euthanized. Cleaning out the tank would be a good idea so it doesn't spread.
But we don't know it's that for sure yet! It could be an internal infection. I just wanted you to be aware of NTD since it requires quick action to prevent it from spreading.
It may easily be an internal infection...I would try Maracyn-Two first. If he doesn't show improvement maybe try Maracyn.
It's also possible he's just bloated...perhaps from over-eating or eating flakes not soaked in water. If that's the case then just fasting him should do the trick.