Hi there ,
Please try to relax.
One harmless possibility of black stools could be eating too much of oreo cookies , chocolate cake , iron tablets or multivitamin
supplements containing iron etc.
The more sinister cause of black tarry stools could be some bleeding in the upper Gastro intestinal tract.
It would be wise to get a complete blood picture and stool examination done and based on the report, get an endoscopy
done, if recommended by your doctor.
Hope this helps.
Dr. Divya Kuttikrishnan