Given that I've had my piggy little neons for a good while now and see this exact same situation on a regular basis, I'd definately suggest just waiting to check the fish in the morning.
Research all you want (you could easily prove me wrong,) but remember to be careful with any chemicals or meds.
I hope your little neon is okay!
Well, I looked today and I didn't see the fish floating or struggling. As a matter of fact, I didn't see the little guy at all. I looked everywhere and started to worry that he may have passed away. Eventually, I found em, hiding inside a rock decoration. Phew. No more big bellies. I can't believe that tetra ate so much. He may have out-eaten my silver molly. So, all is well.:clap: