I think it really depends on the person and their personal tolerance levels. Two people could carry out the SN method exactly the same, but they will have different experiences before they ctb. One could vomit excessively, while the other may not vomit at all, or just a small amount. One may feel pain, the other may not. One might feel hot, tingly, breathless: one may fall unconscious much earlier than the other.
It is important to bear in mind that whilst there may be a common 'end', the journey will always be slightly different.