The AnswerOrdinarily, carbon dioxide is not poisonous. It diffuses from your cells into your bloodstream and from there out via your lungs, yet it is always present throughout your body.
However, if you breathe high concentrations of carbon dioxide or re-breathe air (such as from a plastic bag or tent), you may be at risk for carbon dioxide intoxication or even carbon dioxide poisoning. Carbon dioxide intoxication and carbon dioxide poisoning are independent of oxygen concentration, so you may have enough oxygen present to support life, yet still suffer from the effects of rising carbon dioxide concentration in your blood and tissues. 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.