Hey there, and welcome back to the forums! I'm sure you don't need to be told this, but it's standard to do so around here: I'm not a doctor. I can't tell you what's wrong, or make a diagnosis. I can, however, share my experiences with you, and hope to relieve a little of your anxiety.
Firstly, heart attacks don't just happen. They're caused, predominantly, by a blockage of the blood to the heart, typically from Coronary heart disease. You're not going to have one just completely out of the blue, and without warning. The majority of cases of them are in people with known heart problems, or other risk factors - blood pressure, high cholesterol, diabetes.
Now without knowing your age/weight, it's impossible to know for sure what your recommended maximum heart rate is, but I can tell you that 205 is too much. I think you know that. I'm not sure what you were doing at the time, but my suggestion would be that your body is not quite ready to tackle it just yet. You might want to tone down your exercise a little in all respects, get the numbers down. As a solitary reading that's nothing to worry about, but if you push too much it could cause problems. Build your fitness slowly, there's no rush. This would likely also be why you're having pain, illness. I'd say it looks very likely that you're exhausting yourself, by trying to do too much. A doctor could tell you much better than I could, but I don't think you should be going above about 165, maybe 170 for an ideal workout.