Because the symptoms of carbon monoxide poisoning can be vague and nonspecific, the diagnosis may be missed or not suspected. Headache, dizziness, and nausea are the most common symptoms. Other possible symptoms include malaise, fatigue, chest pain, shortness of breath, vomiting, diarrhea, weakness, abdominal pain, or fecal and urinary incontinence. A number of different psychological and neurologic symptoms can also be present. These can include agitation, confusion, depression, lethargy, impulsiveness, hallucinations, confabulation, distractibility, and memory problems. Visual disturbances and seizure, as well as fainting (syncope), can also be related to carbon monoxide toxicity. Severe cases of carbon monoxide poisoning can lead to coma and death.

Source: http://www.medicinenet.com