I've been struggling with the exact same thing for (sadly) almost a year now. I started to get that strange shortness of breath feeling with a bad body high and also thought I was having breathing problems or a heart attack back around spring break of last year. Before, I smoked everyday and loved it for about 2 years and this came on all of a sudden. I do have an anxiety disorder but weed used to be my salvation from it. I've tried everytihng to get back to normal smoking such as small hits, taking long breaks from smoking, forcing myself to build a tolerance again, smokn alone etc etc and still no help. as for you Jay it sounds like its a lot like what happened to me: you just anticipate that bad feeling to come on so it does. I personally believe its all mental but cant get over it. When i smoke i of course know that theres nothing wrong with me but it just isnt pleasant like it used to be, hard to enjoy it when u feel like u can barely breathe. I would love ANNNNY advice to help me because after a year it still hasnt gotten a SINGLE BIT easier to watch my buddies smoke a blunt or a fat bong rip. And btw **** that guy who says u must be a new smoker to get this, I was about as much of a stoner as someone can be and never got the slightest bit of paranoia when high and this thing hit out of nowhere and i cant shake it.