That happened to me last night in a slight way, the 'seized-breath', holding on to the toke, and then holding onto each of my next breaths too ! But luckily as my guide moved a bit, I relaxed it - remembering to breath easily. I found it natural to just not exhale until I 'remembered to' ... (35 mg, one toke, and it was just enough to make it through, with a very short stay.)
Another time, after the take-off of just 25 mg, I once thought that there is 'a space between the breath' which is where you have to hold it to stay in Hyperspace. As though after taking a huge toke, the normal breathing pattern (a sine wave that never stops) is interrupted, but at the top and bottom of every breath there is an instant where you might poke into hyperspace, and so you 'hang' there, not exhaling.
It's a funnily familiar thing to think/say one doesn't have to breathe in Hyperspace ..! Reminds me of the movie Abyss, where they had to re-learn to breath a liquid oxygen carrier - initially you have to overcome the fear, and force yourself to breathe the stuff, sort of like we all did in the womb.