This is correct. Tetrodotoxin. Like in pufferfish. It blocks nerve signals to muscles causing paralysis. There is no antivenom.

If you got it from eating pufferfish, best you can do is administer activated charcoal to absorb as much as possible that hasn’t already made it into the bloodstream. After that, all you can do is manually run the heart and lungs until it wears off.

So you basically need to be really close to a hospital or clinic, somehow convey what’s happened (while possibly unable to talk or move) and be lucky enough that said hospital has the resources to maybe keep you alive until it is out of your system.