Apoplexy
Following the MRI scan this afternoon my Dad's doctor confirmed a stroke. The type wasn't specified, but the epicenter appears to be the brain stem. The severity of the stroke and the effects it has had on his brain won't become apparent until he is brought out of his induced coma. Something which will begin tomorrow morning.
Again, it's a matter of waiting. If he responds well tomorrow then he may be kept conscious, if not he'll be sedated again.