Law enforcement sources tell TMZ, Kim went to bed early last night, because she wasn't feeling well and when family members went to wake her Thursday she was non-responsive. Paramedics pronounced Kim dead at her home.
As for the cause ... we're told she was battling an illness -- either the flu or pneumonia -- over the last few days and was being treated with Saline and vitamins. Authorities are also looking at a recent trip Kim took to Africa, to determine if she contracted a disease.
No illegal drugs were found.
The coroner will perform an autopsy and perform toxicology tests.