Unfortunately, carbon monoxide poisoning is a real threat. Carbon monoxide is a by product of the combustion of organic materials such as wood, tobacco, and fossil fuels. Thus, we are exposed to small amounts of carbon monoxide all the time without any real detrimental effects. Carbon monoxide is poisonous because it prevents the blood from being able to carry oxygen. Moreover, it actually replaces oxygen in the blood making the body think that it's fine, when it is really suffocating. Thus, carbon monoxide poisoning causes few if any symptoms other than sleepiness before the person exposed slips into a deep sleep and dies. This is why it is so dangerous.
The reason we have carbon monoxide detectors in our houses are because the gas is odorless, it can be released from your typical gas furnace, and people often die in their sleep. A short exposure such as a couple minutes in a garage with a running car will not expose you to enough carbon monoxide to cause any major health problems.
The best type of physician to see about environmental threats and exposures is your primary care physician
. This is the type of question that they are used to answering. I hope this helped your understanding of carbon monoxide and its potential detrimental effects on your health.