2.6 million people die in the United States each year.
Stroke is the fifth leading killer in the United States.
795,000 people have a stroke each year.
I had a friend who had a massive bleeding stroke and froze in mid-stride and mid-sentence, like a statue. He later died after life support was turned off.
The ways for folks like you and me to detect a stroke (aside from the person keeling over) were these until a decade or so ago:
S: Smile — If one side of the face droops or doesn't move, call 911.
T: Talk — Speak a simple sentence. If it comes out garbled, call 911.
R: Raise — Raise both arms. If the person can't, call 911.
About a decade ago it was discovered that there is a fourth sign that a stroke is taking place: the behavior of the tongue. Ask the person to stick out his or her tongue: if it doesn't come out straight, but points off to the side in an odd way, call 911. Oddly this hasn't received the publicity it should.
If you can get a person having a stroke to a hospital and into treatment within a few hours, there are drugs which, if administered rapidly enough, can mitigate the effects. Who knows … you might save a life.