The word stroke has, as one of it's meanings, "sudden action, movement or occurrence". A 'stroke' that you refer to, in the medical sense, is a sudden occurrence of interruption of the blood supply to the brain.
My mum had one a few months back, and they are devastating things. I now think of them as an horrendous "stroke" of bad luck. If there is a God, he/she is not a very nice person to let this happen to such a wonderful human being!
I've also read about them being referred to as "brain attacks" in the very interesting bestseller about 10 years ago titled "How we Die" .....which is really a facinating read.