If there's anything I've learned from smoking it's that these feelings will come and go. I've been at the point where I almost stuck an epinephrine pen into the side of my leg because I thought my throat was closing. You learn a lot about yourself in these situations though. In my opinion they make you stronger in that you are seemingly facing a nightmare scenario at times and getting through it allows you to recognize these feelings in the future and become stronger.

I have asthma, terrible environmental allergies, a deadly nut allergy, etc so I've had my fair share of panic attacks. You just have to open up a little dialog with yourself and rationalize the feelings as they come. The increase in heartbeat is obviously not in your head but you have to remind yourself that you aren't having a heart attack. If you legitimize any of your fears it will only reinforce them in the future. It's a mind game really and although scary it's something I think every pot smoker has experienced at least once.

Personally, I smoke to get rid of anxiety...it's been my nature lately to be very anxious and smoking seems to make everything easier. I'm able to titrate it to the point where anxiety is gone and ambition is up. Although, sometimes when I get absolutely ripped I simply eat everything within sight and rub one off in an epic manner.