When you can't breathe through your nose, you breathe through your mouth. So, how exactly did Mark Gleeson stuffing both nostrils with tampons cause him to suffocate?

[LarsKnowles]

https://www.heraldscotland.com/news/12117183.man-dies-in-bid-to-stop-his-snoring/

He put the tampons in his nostrils before going to bed. He would've been already breathing through his mouth as he was going to sleep.