Breathing in a bit of kerosene fumes short term should not cause any harm to your health as long as you get some fresh air.
However breathing in the kerosene fumes can cause some people to become dizzy or nauseated and if so you should get some fresh air.
Breathing in Kerosene Fumes long term can really affect your health though and cause problems such as neurological or kidney damage, including blood clots that damage the brain, heart or other organs.
So use a Kerosene Heater or Kerosene Appliance with caution and safety and always get some air into the house or wherever you're using the Kerosene Heater or Kerosene Appliance.