Portable Kerosene heaters that are not vented can make you sick if you don't allow some fresh air into the space you're heating with the kerosene heater.
The portable Kerosene Heaters that don't vent to the outside produce carbon monoxide and that carbon monoxide gets into the house or space you're heating and if too much carbon monoxide enters the space it can be deadly to the people breathing it in.
When using a portable kerosene heater that doesn't vent to the outside always leave a window cracked open just a bit to allow some fresh air inside the space to avoid carbon monoxide poisoning.
Portable Kerosene heaters are not meant for a sole heating source but instead are meant for emergency heating.