Carbon monoxide can be in the body at any time, if you smoke or are in a smokey enviroment and passively breath in the smoke it will put carbon monoxide in the blood stream. However, Carbon monoxide poisioning is a different matter IE when you have too much of the stuff in the body this will lead to impared judgement possibly due to lack of oxygen. Remember Carbon monoxide sticks the the red cells better than normal oxygen and then you can suffer a form of Hypoxia. In true CAA style its in the way the question is asked IE having Carbon monoxide in the body rather than suffering monoxide poisioning.
Hope this helps