Hi!Carbon monoxide sources can be gas water heaters, cigarette smoke, gasoline and diesel powered generators, and so on. The risk factors for carbon monoxide exposure include using heating sources /generators or working indoors with combustion engines. In your case there is every possibility of carbon monoxide delayed poisoning
as above mentioned signs and symptoms are commonly seen and moreover when several people in the household are affected at the same time who were previously normal . So be careful in the future!