Ive never had anything like that happen, but if i were put into that situation, it would have crossed my mind that either my friend has some problems with breathing... started hyperventalating because of intense visuals or intense regonition or realization of some sort of truth the individual had been hiding from, or that they were pretending they were having a hard time breathing for some unknown reason.
The only bad trip ive ever had, and only once becase now that ive had one i understand what they are and can now prevent them from happening, is when i tried to make conclusions out of thoughts that had no conclusions. For example; who am i, why am i, questions about "god" When you delve too far deep into questions that have no answers... you may start to make up the answers, some of which are pretty scary... resulting in a "bad trip"
I think a large dose of honesty with self is a must have for anyone to really enjoy a larger dose of cubensis mushrooms.