It can come from any fuel-burning appliance in your home that isn't functioning properly such as stoves, laundry machines, generators, chimneys, etc. It is also expelled by vehicles.
Common symptoms of Carbon Monoxide poisoning include nausea, fatigue, vomiting, drowsiness, elevated heart rate and more. If you suspect you have been exposed to Carbon Monoxide, go outside for fresh air immediately and seek medical help.