Dizziness can be a sign of anemia or dehydration - which can be caused by bleeding and the diarrhea respectively.
I would first see a physician to ensure the above diagnoses are not present.
A colonoscopy would need to be done. Other than hemorrhoids, there are many other serious causes that can lead to bleeding - such as cancer, polyps, or inflammatory bowel disease.
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_b