As I remember, there was a spot you could put a pin and that would cause the blood to enter the head, but not leave it. About the same as putting a clamp on one of the veins. The blood pressure in his head is what killed him: He had too much blood and it ruptured his vessels.
Accurate? I don't know. I don't know much about acupuncture. But as I recall, he removed the pin. I would have thought that with the pressure of the pin relieved, it would have allowed blood to flow normally. Then again, maybe he didn't remove the pin. It's been a while since I've seen the movie.