Hello I am Dr Mittal First, I am sorry about your loss. Stroke is a condition which happens suddenly The blood supply to a part of the brain either stops all together or the blood vessel ruptures. This may happen due to a variety of reasons. I am assuming she had no previously known disease. But consider this- she may have been an undiagnosed hypertensive or diabetic. She may have been on oc pills. She may have had high cholesterol. All such factors, individually or together cause the problem- infarct or bleed. Brainstem carries the main centres for breathing and blood circulation. So any damage here can damage these centres and this can lead to almost instant death. Again, I am sorry for your loss Dr Mittal