I think that if your blood is unable to transport oxygen you will be in a coma, where the brain hasn't received oxygen, for a brief period before you ultimately die. This may last a few minutes to an hour possibly but at some point you will die.
I've read of people losing consciousness in the ambulance that was taking them to the hospital so for some, immediate loss of consciousness does not happen, although the muscles will be deprived of enough oxygen that moving or seeing is impossible.
At that point tips of fingers and lips will be turning blue. Without proper treatment at the hospital the patient would die.
I have noticed, after being on this site for a few years, those who managed to drink a second glass of SN after vomiting were more assured of a swift passage. I want to emphasize it is rare that people survive a large dose of SN without treatment in a hospital.