[DivineMomentsOfTruth]

People who have panic attacks hyperventilate.. they are usually told to breath into a paper bag.

[Grandpa Drudge]

Hypercapnia is the condition of excess carbon dioxide concentration in the blood. Symptoms of carbon dioxide toxicity include high blood pressure, flushed skin, headache and twitching muscles. At higher levels, you could experience panic, irregular heartbeat, hallucinations, vomited and potentially unconsciousness or even death.

There are several potential causes of hypercapnia. It may result from hypoventilation, diminished consciousness, lung disease, rebreathing air, or exposure to an environment high in CO2 (e.g., near a volcano or geothermal vent or under in some workplaces). It can also occur when supplemental oxygen is administered to a person with sleep apnea.

Rebreathing air previously exhaled into a face mask over and over again gradually increases the concentration of CO2 and reduces the concentration of oxygen that actually gets into the lungs. Each exhale adds a higher level of CO2 to the air that remains in the face mask between breaths, accelerating this process.

Hyperventilation, whether from a panic attack or otherwise, would be rather opposite from hypercapnia, with CO2 concentration in arterial blood too low. Thats why breathing into a paper bag helps, to increase the CO2. level in the blood.

Here is a good article on CO2 to help understand it's effect on respiration.

https://www.thoughtco.com/carbon-dioxide-poisonous-607545