Stress can be caused by anything. From peers, to family. From bad days continuously at work to financial problems. Anything that goes wrong can cause stress.
How we deal with stress is important. If you go out and smoke and drink, you're putting a higher risk of getting even more sick than you already are or could be.
Relaxing and Sleeping Having a normal sleep schedule will cease stress on your body. Go to bed at the same time and wake up at the same time each day. Meditation and relaxation can focus your mind on other things besides your issues.
Don't focus all of your attention on your problems. Talk to a psychiatrist or a therapist can help. They can help you sort through your thoughts and issues in an effective way.
If you don't enjoy talking about your own issues talk to others about their problems. It might give you a different perspective on life if someone is going through something worse than you.
People are still currently studying to see if relieving stress can positively help with heart disease. They have done psychological and social studies on this topic. And positive results have shown a down crease in heart attacks.