It appears that you may have torn a vessel in your oesophagus while you had trouble swallowing. The blackness in your stool is likely blood remnants which has mixed in with your bowel motion. If you have a strong family history of gastroesophageal (throat, stomach, bowel concerns), personal history of these issues and presenting with frequent black stools, may I suggest that you visit your local GP in order to have a review. They will do a blood test and may ask you to provide a sample of your faeces for further investigation (An FOB or Fecal Occult Blood check). This would outrule any blood loss from your gastroesophageal (GIT) organs. As you mentioned, you do not feel weak at present. If you do and present with the above symptoms, please do not hesitate to visit your GP or a local A&E service for support. You have nothing to worry about from the incident you share above.