Yeah, I've heard that it doesn't cause brain damage from reputable people in here but don't understand how that could be the case. If you're deprived of oxygen for that long but then you're saved, then surely...?
I think it's because it reduces oxygen gradually rather than cut it off suddenly (like with, say hanging). It takes a while for all (or most) of the hemoglobin in blood to be replaced with methemoglobin. Plus the body is capable of removing a certain % of methemoglobin (that's why we take so much SN, idea is to overwhelm this mechanism). Finally, the striking symptoms of poisoning (bluish skin, nausea etc) occur early, and organ damage starts later. So, especially for people living with others, they're bound to get noticed and rescued before real damage happens.
To sum up, yes it is oxygen deprivation, and I'm 99.9% sure that yes, there is brain damage
eventually. But the underlying mechanism is different from usual oxygen deprivation. Also, I think the time window between brain damage and death with SN is narrower.