I bind around 15 hours a day, give or take, during the week and have absolutely no breathing problems, have never felt light-headed, and have never felt that my body was in danger due to binding. The most I've ever experienced is a little upper back soreness near the end of the day, which I totally expect after 15 hours or so. If you're feeling this horribly after 6 hours, listen to Aero (and now myself) when we say to get a bigger size, because clearly the one you're wearing is too small. Trust me, giving yourself a serious injury and not being able to wear your binder for weeks or months is a lot worse than having a little more chest -- even cis guys aren't completely flat, despite what your dysphoria might be telling you. I'm by no means a small guy and my gc2b binder, sized correctly, has never endangered my health.