It compresses your lungs but not the rest of your body. And no you can’t feel it. Of course I haven’t been that deep, I stopped at just over 100 feet.
Going 300+ feet deep with or without air tanks is dicey and the margin for error is razor thin.
Yikes! I used to go to 20 meters which was work without wieght, enjoy some bottom time and then kick like hell back to the surface. The more I read about blackouts, the less I was tempted to push it. Getting cautious as in my middle age.