I'm a little late coming to this discussion, but will add a few things to the good advice you've already received.
I haven't had an MI, but did have a 99% blockage in my LAD with a stent placed about two weeks after my 54th birthday. This was not a birthday present I appreciated. Luckily, I had classic angina symptoms that I recognized as such and ignored for only about 10 days. If I had had an MI I likely would be dead, given the location and severity of my blockage.
I too thought I was way too young for this, and was perturbed that most of the literature, support groups where they exist, etc. are geared toward men in their 60s or 70s or whatever. I was especially perturbed to find that there are no prominent spokespeople who are younger women (Patty Duke, where are you?) to get out the word, and that the media still focuses on breast cancer while heart disease kills 10 times more women, including younger women.
I am absolutely convinced that extreme stress was an important factor (along with other risk factors like low HDL and family history) in my developing heart disease young, partly because I know of at least 5 other women my age or younger who have/had heart disease who worked for the same agency. (Unfortunately, two of them are dead as they did not survive their first MI). So, lower your stress level however you can is my best piece of advice.
The depression and anxiety, as others have said, is normal. But denial (at some level) usually comes first. Just be aware that everyone grieves differently (and that is what is happening; we are grieving the life we had or dreamed we would have and learning to cope with the new circumstances). I too eventually tried Zoloft, but I could not tolerate the side effects (second time in my life I tried an SSRI; never again).
Now, more than 3 years out, I rely on the occasional Valium if the anxiety becomes too much (which occasionally it does when I'm trying to figure out whether the discomfort I'm feeling my chest is GERD, gas, angina, etc.). I'm less anxious now, but I too think I will always be hyper-aware of my chest and scared if I feel a chest pain.
While it is important to eat a healthy diet, avoiding all fat is not necessarily good. Minimizing saturated fat and avoiding hyrdogenated fats completely should be your primary goal. While some people do well on Ornish type diets, others claim they actually see a rise in their lipids. Most people cannot stick to such a severely restrictive diet long term. Something along the lines of the Mediterranean diet, the Weight Watchers Core Plan, or South Beach is probably more do-able long term. I avoid full-fat dairy, and try to minimize beef and pork, but I haven't cut it out completely: there are some cuts of beef and pork that actually have less saturated fat than poultry. I allow myself a couple of slices of center-cut bacon once per year, and once a year I have a fried chicken meal (that I fry myself in canola oil). (I'm not willing to live the rest of my life without occasionally eating some of my favorite foods).
I could go on an on about an number of issues: suffice it to say I think I do know how you feel. You are just beginning a new journey in your life. It will get better with time, but it will always be different.
(BTW, I had to stay off the boards for awhile, and still do much of the time, because they were just too anxiety provoking).