Yep, sorry it happened to you, they really do suck and are terrifying the first time. Even though I know I'm fine, sometimes the anxiety still makes me unsure, it is a rough thing, and the more you worry the worse it gets.
I feel for you, I really do. Becareful with too much hydration though, that can cause water intoxication and kill people. A good test is your urine. If it is dark, then you are dehydrated, if it is clear, you have drunk too much water, the ideal color should be like light yellow/partially clear. Another thing to avoid water intoxication, is to drink things like Gatorade, sodas, juice, anything with sodium in it. If you drink these instead of just water, it helps to prevent your electrolytes from getting crazy which is the main problem with over-hydration. Or just eat salty food with regular water.
But don't feel free you can't exercise either. I lift weights, dance, and walk for hours at a time on and off stimulants, and I'm fine. In fact exercise with meth is a great idea because you get the energy and motivation, and it helps with the comedown immensely. You can also get panic attacks from not even using drugs, I do. It is just something that happens to some people. I never use to get them, now I do, which blows.
Something to strongly consider is getting a hold of some benzos for when these panic attacks are really bad. Alcohol also works, but not as well. Of course the problem with this is if you are using meth to stat the day and benzos to end the day, it can be a really bad habit, so I recommend just using the benzos when it is really rough, like a multi-day binge or a stressful time in your life.
In summary...
+ Go to the doctor and get your heart checked out. When you find the results are fine, use this as re-assurance during your next panic attack (although hopefully you don't get them again).
+ Possibly consider getting a device to measure blood pressure and heart rate to ease your fears, although this can become a compulsive thing so I wouldn't recommend it as anxiety can make you doubt everything.
+ Healthy diet, exercise, try to get some sleep will also reduce these problems, as well as avoiding mixing too many stimulants and having benzos on hand.
+ Realize an actual heart attack you won't be able to move around at all, and if you can talk, you can still breathe, use this tactic to help fight your mind from tricking you.
+ Get to the source of panic attacks. Usually they are a subconcious way of our minds telling us we aren't taking care of ourselves.
+ Even though it is hard, try to distract yourself with something else. The more you try to not think about it, the more you will think about it.
+ Try belly breathing. With panic attacks we tend to breathe from the chest instead of the stomach, so you get the tightness from muscle soreness, not actual heart problems. (read here for more info:
http://www.anxietycoach.com/breathingexercise.html)
+ Get your boyfriend to rub your chest. This can greatly reduce the chest tightness as the muscle that causes this feeling is sore and needs relaxation.
Other than that I'd say you could lay off stimulants, but in my experience, it doesn't make much difference. Sorry it happened to you, I have the same problem and it does suck.