Fresh blood from the eosophagus tends to be red/dark red not black because it is not denatured. If the blood was a clot it may be very dark/current jelly but it will come out and then typically red/dark red blood will follow.
Blood in the stomach comes up usually looking like coffee grounds [useful to look at it in a white dish and to roll the liquid around to see the little specks. If you have recently [within a couple of hours drunk a black stout or dark red wine, it may well be that. So, don't worry it is most likely that after recent consumption. However, go to the doctor to make sure.
Obviously you have some concern about the effect of alcohol. Indeed alcohol can cause bleeding. This is usually due to damage to the liver and changes in the blood supply and pressure. This damage can also be caused by hepatitis and certain drugs/meds. So, you should discuss all this with your doctor. As if you are concerned about your drinking you can avoid major medical problems by acting quickly at this stage.
caveat - I am a scientist not a medic - so while this information is based on the best research I have to hand you need to be properlly diagnosed and treated.
My suggestion would be to go RIGHT to your doctor, or better yet, to a Gastro doc, because vomiting up anything black is not a good sign. Many years ago, my mother had that problem (and NOT a drinker at all!) as well as black tarry stools, and it was because she had bleding in her stomach. She ended up in the emergency room, and had surgery a few hours later to try and repair the damaged/bleeding area in her stomach. Over the next week she had 5 more surgeries, and finally they were able to conrtrol it, but not before she lost half of her stomach because of it. She was in the hospital for 56 days, and finally came home, but a few months later had more complications with adhesions. Anyway, I know I probably scared you to death saying all this, but it's better to get checked out BEFORE something horrible like that happens to you. Please take care.
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