Been smoking for like 20 years. Had a daughter in 2018 and since then I have been getting anxiety and panic attacks almost every time I smoke. Needless to say, I have cut back big time. Went from dabbing like half a g of concentrate and a few grams of flower a day to barely being able to take a few hits. It's crazy. Had a very similar experience to what you mentioned OP. Initially I thought I was having a heart attack, went to ER and everything was fine. Didn't realize it was from the cannabis so I continued smoking... I'd get anxiety and then smoke more to try and combat it, always worked before... but then come to find out it was the cannabis causing it. I occasionally had good days where I could smoke a few joints, but then other days I'd smoke a quarter of a spliff and then have 2-3 hours of straight panic... 200+ heart rate, elevated blood pressure... all the signs of a heart attack. I'm generally healthy, a little overweight... Doctor says its cause I went through so many life changes in a short period of time... over 12 months had my daughter, lost my Dad to cancer and my dog died of congestive heart failure. I didn't really believe him at first, but I can't think of any other ideas. From research I've done, I guess I could have damaged my CB1 receptors from smoking too much... My friend and I have done a lot of talking about it and we think that having my daughter opened up new pathways or something, and now the THC is connecting to the receptors in my Amygdala (apparently the part of your brain that deals with stress/anxiety etc.) I read somewhere that for whatever reason your body can start processing the THC differently and prioritize what parts of your endocannabinoid system get the THC first, or what receptors are the most receptive... I have no idea. lol. I still enjoy cannabis through site and smell, sometimes I'll do a fat dab of some really terpy shit and just not inhale as best I can. What I really miss are the terps. Hopefully one day they can come up with some conclusive information as to why this happens. In the meantime I am going to keep trying to figure it out. Been almost 2 months now where I haven't really smoked at all, trying to reset my system... funny part is that I still feel high all the time. lol.
*Edit: Doesn't matter what strain I smoke. Indica, Sativa, whatever... sometimes I can smoke one strain and I'm fine, the next day I get anxiety. And CBD does nothing for me at all.