My mouth just filled with dark red blood?

Dear All, i am 32 yr old male. have a no real medical history of illness apart from i suffer with anxiety and depression for which i currently take no medication.
over recent months my insides have not been working constantly well and i often have constipation and diarrhea. i do have aches in my stomach and insides and it is often bloated after food and alcohol.
today i was sitting at my desk and my mouth just filled with dark red blood and a single clot the size of a 5 pence piece. i have no signs of any blisters sores etc in my mouth.
i am a heavy smoker and exercise little.

please could you advise

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