Happiness, true happiness, is an inner quality. It is a state of mind. If your mind is at peace, you are happy. If your mind is at peace, but you have nothing else, you can be happy. If you have everything the world can give - pleasure, possessions, power - but lack peace of mind, you can never be happy.
Everyone has the ability to increase resilience to stress. It requires hard work and dedication, but over time, you can equip yourself to handle whatever life throws your way without adverse effects to your health. Training your brain to manage stress won't just affect the quality of your life, but perhaps even the length of it.