Yes and Yes. Stress is always a factor in any disease or medical condition. If you have a strained heart than additional stress could be enough to tip a person into a heart attack. High stress levels can also decrease a patient's will to live or just depress their body functions enough that they don't survive. There is a famous story of a man who was given only 6 months to live because his cancer was terminal. He ignored his doctor's prognoses and started watching 3 Stooges films. He literally laughed himself into a longer life. He is dead now, but he bought himself a few years. Stress Kills, plain and simple. It takes any problem that you might have and makes it worse. When we are under stress we have the "flight or fight response" adrenaline is released into the bloodstream and the body responds with an increased rate of activity, a lowered pain threshold and a more streamlined response from your body systems. The situation becomes one of over-revving an engine. If you run an engine at 120% then you will be putting it under too much stress and increasing the chance for a failure. Your body is a complex machine and over-revving it only increases the chance of a breakdown. The longer you subject yourself to high stress the longer you are over-revving and running your engine too hard. Worrying too much is another way of increasing your stress. If you are a very healthy person than you can function at that rate for a long time, but just like a NASCAR racer if you keep racing you are going to have a major failure. The older your engine is the worse such a failure could be.