> However, it’s important to note that rebreathing is unsafe for certain people, particularly those with heart or lung problems. Having too little oxygen in the blood, which is known as hypoxemia, can share symptoms with an anxiety attack. These include shortness of breath, dizziness and rapid breathing. If someone experiencing hypoxemia practices rebreathing with a paper bag, they’re not only making their immediate condition worse, they’re putting themselves in danger. The bottom line is, unless you know beyond a shadow of a doubt that you’re hyperventilating due to an anxiety attack, leave the paper bag maneuver to the TV writers.

The last paragraph and really the last line are the most important here. While it may work, it will only work if you're actually having a panic attack. Otherwise you're just doing yourself harm.