Every now and then I do one as well, while lying down in bed. Based on Wim Hof: 30 quick breaths, breathe out and wait until you get the urge to breathe (can take a while), inhale fully and tense all your muscles for 15 seconds, release your muscles and breathe out.
It can cause fainting. Maybe I don't sleep, maybe I just faint for 7 hours.