Adverse effects from Marijuana?

I started smoking when I was about 16 or 17, I am 20 now. A few times through out my smoking days, I've had my heart rate accelerate so that it feels painful accompanied by nausea and dizziness. It seemed that it had gone away for a while, but it seems to be recurring in the past few weeks, especially yesterday. I just smoked a couple bowls with a friend, and soon realized I was way too high. I know that it isn't uncommon for your heart to pound here and there, but is it something to be concerned or worried about? I was born with a slight heart murmur, I think a "2 out of a 5" on a scale, but they never really did anything about it. Yesterday I was so dizzy and nauseous that I couldn't close my eyes. I tried to focus on a spot and keep staring at it. It was strange because I felt so tired but closing my eyes made me overwhelmingly sick feeling. Many of my friends never seem to have their heart race, or at least don't mention it. The only person I've ever met who talked about is was my friend's mom who was like 50. I consider myself in pretty good health, besides that I am smoking.

Do you have any advice on how to counter this? Or what may be causing it? Smoking in the day time hours, which I did yesterday, always seem to get me much higher, but yesterday was a horrible feeling. I smoked at around 4 and felt horrible for the rest of the day, even today I felt groggy and unwell. The weed was pretty good stuff, but I don't think it was THAT good. I also suffer from depression and anxiety, though that is more of a self-diagnosis because I don't go to a shrink (yet). Can something like not having eaten earlier that day have an effect?

Sorry if I posted this to the wrong forum, I'm new here. Thanks guys.