What Could Cause Only Blood Discharge During Defecation Apart From Weakness And Dizziness?

Hello i have been going to the toilet for the last 48 hours and all I discharge from my bowls is pure blood. After this I feel very week and dizzy for about half an hour. The blood is mainly a bright red with a few clots of darker blood. I am very worried and don t know what to do. I am also out of breath very easy even when walking. I am a 45 year old male.can you help