CT Scan Shows Probably Microvascular Ischemic Which Is Chronic. History Of Stroke. What May Have Done This?

my father had a ct scan yesterday that says on results report he has probable micro vascular ischeamia which is chronic he had a mini stroke 15 months ago but recovered completely and 5 weeks ago a sudden change caused him to go from fairly active (sitting on computer for 2 or 3 hours daily communicating with family and friends, going to breakfast 3 or 4 days a week with mom and neighbors, light yard work, attending meetings where he held a board position locally) and suddenly inside of 24 hours he got confused, unstable walking and deterioriated to not able to walk at all with assistance and speech unclear, sleeping 23 hours out of 24... no one can tell me why this drastic change occurred over night and didn t correct. What may have done this?