you friend was right go see the doctor ASAP
Black liquid usually means old blood. I'd see a Dr. immediately.
I hope that you are gone by now because that is exactly what you should be doing.....this is no joke here .......it can be serious ....................................
Blood that has been sitting in stomach and partially digested turns black. Thats why it isn't red like if you had cut yourself. Get to the doctor .....yesterday.
Ok thank you very much everyone