My brother lost consciousness for up to a hour and had no memory of the previous two days. If this was the result of lost of blood to the brain (?) what could be the causes? He is 65 and probably overweight but otherwise fit and has no symptoms other than an enlarged prostate
HIT hanks for posting your query to Chat Doctor.  There are quite a few causes for such Unconscious spells. I will tell about few common causes. 1. Seizure Disorder : A condition which causes convulsions (fits)2. Stroke : Inadequate Blood Supply or Bleeding inside the Brain.  Cause for Seizure is Electrolyte Imbalance (Low / High Blood Sodium, Calcium Magnesium levels, Low / High Blood Sugars), Infection spreading to Brain, Some Mass in the Brain, Epilepsy, Liver Failure, Kidney Failure.  Cause for Stroke are Uncontrolled Hypertension, Uncontrolled Diabetes, Elevated Cholesterol, Smoking, Alcoholism, Disorders in Blood Coagulation.  I advise you to get MRI Brain, Serum Sodium, Calcium, Lipid Profile, 2D-ECHO and revert with reports.