This study points out how increased blood levels of CO2 can be at the basis of the 'flight or fight response' in panic attacks. I have often thought that CFS sufferers are mainly 'shallow breathers' due to our lower activity levels. This can increase CO2 blood levels and could explain some of the 'flight and fight' symptoms, of which the panic attack is the ultimate response. We take deep breaths as a natural response to panic attacks and this lowers CO2 levels and lowers the symptoms. Regular breathing exercises every day I find helps to keep CO2 levels lower throughout the day and this cuts down on the number of 'flight and fight' symptoms.