When I was recovering from PTSD, my panic attacks likely included hyperventilation. At the time, I thought it was a new case of asthma since it felt like I couldn't get enough oxygen, making me feel faint. I had to go through therapy, flashbacks and all the rest plus be put on many medications. Since I thought it was asthma (I don't have this--anxiety makes you think you have all kinds of stuff), I did not try the paperbag thing but will if it ever comes back. Anxiety attacks make you feel so out of control and powerless. Sorry you are dealing with this....