I would continue to watch it or quarantine it....Pleistophora hyphessobryconis is usually first seen as a loss of red colouration in neons, followed by a failure to school, then swimming problems....your neons symptoms certainly sound suspicious. Just remember that this is a very easily transferrable disease, so the other fish may already be infected, so keep a close eye on them as well.
G. A. Christian Bilou, Herpetologist
Founder/Director, Reptile Rescue Alberta
Past-President, Calgary Aquarium Society