You are so young...........I'm very sorry you had a heart attack.
If you haven't already, please let your cardiologist know about the tightness you're feeling and also the highly emotional state you're in. Many people who have suffered heart attacks become very anxious, even depressed and these issues need to be addressed as they will affect your overall health.
Many hospitals have classes for people recovering from heart attacks, which include support groups and exercise classes. I think these classes would be a very positive activity for you to get involved with. You would be around people who understand exactly what you're going through and the exercise classes are geared towards cardio rehab. Get a check up from your cardiologist and explore what you're community has to offer. If the fear and crying continue and are interfering with your daily life, then it may be time to look into some therapy so you can begin to enjoy life again.
I understand your fear, at least, I think I can, but sitting around waiting for something bad to happen is blocking you from all the good that WILL happen if you get pro-acive in your healthcare. Millions of people have had heart attacks and go on to live long, full and happy lives. Why shouldn't you?
Please let us know how you're doing, OK?