OP are you familiar with the fact that if you breathed compressed air at 10 ft, then ascended rapidly while holding your breath, you could suffer an air embolism which could cause an air plug which would stop bloodflow to your brain and give you a stroke? People don't usually survive strokes or heart attacks underwater either.
This is the most basic part of risk with SCUBA. It all builds on that.
Simply put : IF YOU HOLD YOUR BREATH ON COMPRESSED AIR, YOU WILL BE INJURED OR DEAD
This is just one of the many risks. I encourage you to pursue proper training in a controlled setting.
But, it's your body. Do what you please with it.