Okay lot's of sarcasm of course and there is nothing better than getting properly fitted. However, it is possible for one to be properly fitted with a stem with some rise, and due to improvement in fitness and body changes, want to get a few centimeters lower. And that IS something you can try without the professional help of a fitter. (Often times, going lower can mean going to a shorter stem, so don't flip it, ride it and immediately say it doesn't work.) So, if you feel like you are properly fit on your bike and want to flip the stem to a flatter rise, go for it. You got nothing to lose.