It happened when she lighted an aroma theraputic candle for the night in a room with the air-conditioner ON. Due to subsequent lack of oxygen in the room, the burning of the candle cannot fully oxidize, thus forming dangerous carbon monoxide.
Carbon monoxide will prevent oxygen exchange in the lungs, resulting in the person dozing off into a state of unconsciousness & eventual death in less than an hour, depending on the room size.
