YO! I've had the same happen to me.THIS!! I have the same reaction. I think I’m having a heart attack and my mind starts going to some other shyt. I start thinking about death, hell and war and other bad things. Thought my brain was melting. Reason why I don’t smoke.
Same reason I don't really indulge in hallucinogens that much anymore...it has my thoughts racing and it's like if you get stuck on one negative thought that shyt could ruin the rest of your trip.