carbon monoxide
Carbon Monoxide is the result of incomplete burning of carbon compounds (such as a banked wood fire). The gas is colorless, odorless, and tasteless. Some symptoms include a dull headache, weakness, dizziness, nausea or vomiting, shortness of breath, confusion, blurred vision, and loss of consciousness. Carbon monoxide poisoning is particularly dangerous for sleeping people since they may die without ever awakening. If you believe you're being exposed the carbon monoxide, the first thing is to GET TO FRESH AIR IMMEDIATELY, then seek emergency medical care.