Learn to recognize the symptoms of carbon-monoxide poisoning. Many victims of CO poisoning are misdiagnosed because early stages manifest symptoms similar to a cold or the flu. Unfortunately, the true diagnosis often comes too late. When the COHb level in the blood reaches 10 percent, the symptoms are headache, dizziness, weakness and loss of coordination. As the level of COHb rises, the individual will suffer nausea, vomiting, sleepiness and confusion. At a level of 40 percent, the victim will collapse, and at 60 percent death occurs.