Hi there, Thanks for your query. In view of multiple diseases and several surgeries, it is difficult to hazard a guess regarding dizzy spells, without further information and test reports. However, the possible causes can be either, intermittent low blood sugar, involvement of autonomic nervous system as a diabetic complication, a minor thrombotic stroke involving part of the brain regulating posture (in view of clotting disorder), salts imbalance in the blood; or, spread of cancer cells (presuming colon tumor to be cancerous) to the brain. Consult a Neurologist and apprise him of my opinion. He is the best judge, who would be able to pinpoint the cause of periodic dizzy spells and imbalance, after examining you. If you find my response helpful and informative, do not forget an “excellent” (5-star rating) to my answer, to ENCOURAGE ALL doctors- engaged in social service- to render sound advice to the FREE queries. Take care Dr. Rakesh Karanwal