Hello,
What your husband actually suffered from looks like Syncope. For syncope/
fainting to occur, either the reticular activating system in the brain needs to lose its blood supply, or both hemispheres of the brain need to be deprived of blood, oxygen, or glucose.
So it can be due to fall in BP, hypoglycemia, dehydration and inadequate electrolytes(sodium and calcium) in the body, postural hypotension, blockage of arteries supplying blood to the brain esp.