I'm not worried about it. I believe unless something goes really wrong, you won't be conscious enough to realize you have breathing trouble if that happens.
I've been thinking about the people who appear to have respiratory distress. One thing to keep in mind is we mostly have no idea how those people breathe normally when sleeping or passed out. It could be like snoring. Sounds really bothersome to observers, but you don't notice it much yourself.
I have sleep apnea. My last sleep study had me logged as having up to 90 breathing obstructions per minute. That's beyond excessive. But it's apparently standard for me, and I'm not aware of it 99% of the time. My only real indicator is I'm always so exhausted. Anyway, I guarantee anyone witnessing that would freak out, thinking I was really suffering and not able to breathe when I'm really oblivious. And that's just sleeping. So while unconscious from SN, I'm betting it looks and sounds a lot worse than it is for the person. Even moaning, it doesn't mean you are aware of the feelings. It's just the body's responses.
I'm also basing this on survivors reporting not feeling too distressed and having little memory of it. And willingness to try SN again.