Sodium Nitrite, NaNO2, acts as a catalyst in the conversion of the hemoglobin in your blood into methemoglobin (MetHB), a molecule with a much higher affinity with oxygen. This occurs when the ferrous ions in the regular hemoglobin are converted into ferric ones.
Since it's affinity is so high, methemoglobin cannot let the oxygen flow into other tissues that need it, thus depriving them of oxygen even while you're breathing. Death, then, occurs by hypoxia.
Sodium Nitrite poisoning symptoms include nausea, vertigo, vomiting, very heavy headaches and, should you manage to not pass out for too long, seizures.
The PPH claims that, during a monitored suicide with SN, the patient was unconscious at 12 minutes and dead by 35. However,
some sources claim that SN poisoning might take as much as 8 hours to kill, probably due to low dosage.
Since methemoglobin creation is a natural process in our bodies, you must be aware that a certain enzyme works to transform it back into hemoglobin again. This is why the recommended dosage has varied on the PPH so much, as the syntetization of these enzymes and their "power" to overcome the formation of MetHB depends purely on your body, thus making a normal, general dose for all who chose this method very hard to determine, unlike N.
As for the physical symptoms your body will experience, not much will really change. Since your blood will mainly be MetHB, it will take on a bluish chocolate brown color, and the tips of your fingers, toes and nose (amongst others) will turn slightly blue from cyanosis.
