See e.g. http://www.normalbreathing.com
CNS/Diseases of the Brain Are Caused by Low Brain O2/CO2 Levels
http://www.normalbreathing.com/diseases-Brain.php
Sedatives | CO2: Natural Sedative and Tranquilizer http://www.normalbreathing.com/CO2-stabilizer.php
After 15 years of panic attacks, anxiety, migraines, hay fever... if finally found the solution: learn to breathe correctly again. The best and cheapest thing I've ever learned for my health!
This is just one site, but there are many more on the web. Not affiliated to a single one of them, but hopefully I can share the joy of a panic attack free live with at least one other person. :)