Know the symptoms of carbon monoxide poisoning. At moderate levels, you or your family can get severe headaches, become dizzy, mentally confused, nauseated, or faint. You can even die if these levels persist for a long time. Low levels can cause shortness of breath, mild nausea, and mild headaches, and may have longer term effects on your health.

Since many of these symptoms are similar to those of the flu, food poisoning, or other illnesses, you may not think that CO poisoning could be the cause.

If you experience symptoms that you think could be from CO poisoning:

GET FRESH AIR IMMEDIATELY. Open doors and windows, turn off combustion appliances and leave the house.
GO TO AN EMERGENCY ROOM and tell the physician you suspect CO poisoning. If CO poisoning has occurred, it can often be diagnosed by a blood test done soon after exposure.
Be prepared to answer the following questions for the doctor:
Do your symptoms occur only in the house? Do they disappear or decrease when you leave home and reappear when you return?
Is anyone else in your household complaining of similar symptoms? Did everyone's symptoms appear about the same time?
Are you using any fuel-burning appliances in the home?
Has anyone inspected your appliances lately? Are you certain they are working properly?

Source: Environmental Protection Agency