Death by an Aneurysm?

I had a friend who died due of an Aneurysm. His death was instant, no warning, aside from a headache that started about 14 days before he died.

I have done a bit of reading yet remain confused. I have read that a Aneurysm is weakness in the wall of a brain artery, It then ruptures.

I can understand that this could lead to loos of ability to function and maybe even to kill a person over time as the blood gathers around the brain, (that is the person would begin to lose control of things as areas of the brain are affected) but I don’t understand how it can kill in an instance.

This is where my confusion comes into it. How can a person be functioning as normal, then be dead before he hits the floor.

It was like someone turned off a light. Now you see it, now you don't.

What happened to kill him so fast?