Carbon monoxide poisoning happens from breathing in carbon monoxide (CO) at large levels.[1]
Symptoms are often described as "flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large exposures can result in loss of consciousness, arrhythmias, seizures, or death.[2]
Carbon monoxide poisoning can be accidental, like if the oven's gas is left on by accident or a gas leak. However, it can often be used as a suicide method such as keeping the car on while in a closed garage.