Sounds familiar and very much like the couple of times where I've dosed around the threshold of breaking through, which for me is around the 4-5g mark. I remember that both times it felt like I couldn't breathe unless I did so voluntarily, but if you manage to actually break through from such a dose your body will look after itself as it should. I've even had the sensation of being told "you shouldn't have held back, you're going to miss out this time!" on the last occasion.
I keep away from such doses now, either doing more - at least 6g when aiming for a breakthrough - or doing less - between 1-3g when just getting trippy on shrooms alone, or less than a gram when mixing with other substances. That's what works for me and not a recommendation.
The stars keep burning,
Worlds keep turning,
Through joy and pain,
Forever learning.