Let's think a moment about being buried alive for a zombie ritual. You are drugged to the point of "apparent" death and buried (and according to numerous victim accounts over the decades, fully aware, yet paralyzed) Ask yourself: how do you think it would affect you after the drug wore off & you spent your time panicking and screaming for help in a coffin underground, wasting your oxygen scratching with your fingers at the wood above your head to the point of bloody nubs?
Is it the toxin or lack of oxygen that causes the brain damage, keeping in mind that actual medical facts dispute your claim that it's the puffer poison?
I know it's more fun to see it with the zombie spin, because the reality of it is simply much more boring.