If you experience any of the above symptoms listed or your CO alarm is triggered, the United States Consumer Product Safety Commission says to: Never look for the source of the CO leak. Move outside to fresh air immediately. Call 911. Do not re-enter the premises or operate any appliances until the emergency services responders have given you permission
Even if the alarm is sounding and you only have mild symptoms, such as tiredness or a headache, it's not worth ignoring!