What do you do if you vomit, abandon attempt like PPH says or take more SN?
I'd try to throw up everything and try again when things have settled down. But just like
@Raggas said, death is still fairly likely if you take the full 25 g if you don't vomit it out right away.
Right now I'm leaning toward the tourniquet method with an actual combat tourniquet. But If I went with SN, I'd probably split the 25 g dose in two, take the first one, and if all feels "good", take the second one. I wouldn't want to do the 48 hour regimen, so I'm a bit worried about vomiting as well, even if the PPH has stated that vomiting is only a possibility, not a certainty, and that's without antiemetics. Perhaps this has changed in the latest revision, I haven't had a chance to look at it.
Having an empty stomach and not being very anxious probably would help matters. Although the latter one can't really be helped, I'm afraid. I think even the most nihilistic, depressed edgelord would be very, very anxious when he/she is taking a deadly poison. I know I'm a nihilistic edgelord, and no matter how much I say I don't care whether I live or die, I know I'll be very anxious. I don't have any meds to combat this, either.
So anyway, I wouldn't worry about vomiting
that much.