A lot of red wine or taking bismuth (pepto bismal) can cause dark stools as well.
the black stool may be due to internal bleeding in stomach area and if yiu have vomitting sensation too then bleeding may be in esophagus also due to varices.better to consult gastro speacialist immediately.
with regards
shanmugan
If indeed your motions are black/tarry from upper intestinal bleeding then the medical name is MELENA.
You may like to look this up on google/yahoo etc to learn more.
Prompt medical advice would be appropriate but unless you are expelling significant quantities of blood (~100 mls+) ex rectum then it is not an emergency.
regards
Morecambe
Also, I forgot to mention, about 10 minutes after the black stool I had to use the bathroom again. There was much, much less stool this time but it was brown, not black.