Hi Chojek,
I havn't had a heart attack but I do have the same sympthoms as you. I get it when I relax (or worse when I "try" to relax). I sometimes also get pains in my arms and tightness around my chest. Eventually I belch and they go away. Freaked me out so much that I have had these checked out and its pure anxiety (for me!!!). In fact they've gotten worse since I became healthy, fit and lost a ton of weight!!!
I get anxious relaxing smoking dope (particularly lying down, but also sitting) - I put this down to the subconscious finally getting a chance to shout at me!. I've had to learn not to bottle things up (lots of small things can be much worse than one large issue - that can be easier to deal with) and not to do drugs when I've shit on my mind.
It came to a head when I started coming up I started having palpitations, paranoia, shivers, ear-squeezing (but not popping) and my shoulders being squeezed together every 15 to 20 minutes for 4 hours with no high = which left it a bad night for me and I peeved my friends off (again too much on my mind). I called it "intense". A week later after I had the worst panic attack of my life, where I really thought I was going to have a heart attack and it brought me right back to the feelings of the intense comeup, but this was much worse - I knew I had to keep walking to warm up and stop the shivers, but the more I walked the worse it became, but I finally realised that I needed to control my breathing and that what I was blaming on drugs (they didnt help) was really me being shown that I need to sort those problems out.
My advice to you is to lay off drugs for a while (its a bitch I know I'm trying too), Grass doesn't help either, and in most cases can be worse, for you. do your research to put your mind at rest (I sometimes take my blood pressure/pulse if I'm smoking and get the feelings, but that'd look silly in a club!!!) I'm also learning to control my breathing and meditation (music can now make me feel like I'm high when I do this without rolling) and after a break start again staying with small doses - again why I only roll with 1/2's now and trying to keep it every 6 to 8 weeks and get the best highs of my life from very little.