My grandfather does the same thing. Several years ago, he got sick and needed to spend some time in the hospital.
Since there were no fields to plow, tractors to fix, or chores to do in the hospital, he decided to hold his breath and see how low he could get the oxygen level on his monitor to go.
Monitors started beeping as his oxygen levels fell. Grandma became annoyed with him for playing around with the equipment and not taking his illness seriously.
So it’s genetic and/or learned.
