Heart health problems?!

For the past couple of weeks my heart has been beating too fast, it hurts every now and again and sometimes makes it hard for me to breathe.. I have also been getting a lot of dizzy spells..i was wondering if that's related?
It may be because of the amount of overdoses I've had..or could it be something else?
Sometimes it feels like when people describe what a heart attack feels like... What do you think is going on? What should I do? It hurts waaaaay too much...