How do you know if you have mild co poisoning? small fire in my house last night. woke up by the fire alarm. i was in a different room. but a lot of smoke and smell in the other rooms. no symptoms. but worried about potential effect on brain, heart?

Whether or not one experiences carbon monoxide poisoning is directly related to the concentration of the carbon monoxide and the duration of exposure. If you did not have very early on symptoms dizziness, nausea, confusion, etc., then I doubt you have had any sort of significant nor long-term problems. Carbon monoxide is quickly removed from the system once one is removed from exposure.

Carbon monoxide poisoning can occur acutely or chronically, and does not sound like either occurred with you. If worried, a blood test, carbon-monoxy-hemoglobin, could be obtained. You should possess CO detectors where you live, as these are different than so-called "smoke detectors", but sometimes both are combined in one unit.