Anoxia. Carbon monoxide if inhaled, fits into the oxygen carrying site on hemoglobin even better than oxygen. This means your body will be deprived of this critical element. It is as if a tourniquet were applied around your neck. You will appear bright red but since the redness is from the wrong chemical, your cells will die due to oxygen lack. This is an extreme emergency.
Headache. Headache and nausea are the first two symptoms most people experience. Confusion and coma can follow quickly if it is not recognized.
CO exposure. It depends on whether it is acute or chronic and also the severity. Acute severe exposure as might occur to a person who was trapped in a house on fire can lead to coma and ischemia of vital organs including the brain with brain anoxia. Chronic lower grade exposure can lead to headaches, nausea, fatigue. Etd. Pets my have symptoms too if they are exposed to carbon monoxide.