I Had Diarrhea And Vomiting Last Eve. Dizzy, Faintness. Went

I had diarrhea and vomiting last eve. Dizzy, faintness. Went to bed. I thought it was food poisoning from a quiche I'd kept too long. Expected to awake feeling ok. Insteard dry heaves and more liquidy, but bloody, rectal discharge. Rested most of day, ate little. Sat up on computer, Weakness got worse, urinated, then bright red bloody rectal discharge. I have no idea what this could mean, or who to call, if anybody. I do live alone, am active, 70, and healthy up to this episode. Can you give me more info, so I can plan my next step?