If you're conscious you'll just pull the mask off if you start feeling like you are not getting the right air. These machines, and masks, have all kinds of safety features and safety valves on them.
I have a CPAP, oxygen concentrator and assorted hoses and masks, and I've messed around with them these days while watching ventilator 101 videos on YT. If you're a technical person, the basics are not that hard to grasp.