Alright i happen to be extremely experienced in this area.
Dopamine which is what weed releases
in the brain is an anxiety drug naturally
produced by the brain.
It's is the cause of the same feeling before stepping on a roller coaster or before sky diving, etc... Most of these guys in here are going to tell you aww man your a pussy you can't handle your weed blah blah blah! Stoners are extremely egotistical i can say it because i've been there...
What you had was a serious anxiety attack, i have had many and they eventually forced me to quit smoking. I still end up smoking about one month out ot the year, because i miss the taste. but it usually ends the same way, me thinking im going to die.
The last time my heart actually was racing excessively fast which was confirmed by the people i was smoking with who were completely surprised, they just thought i was freaking out, but it is physical. i felt a numbness go down my arm from my left armpit. I felt it go up my spine into my head and all the sudden i was experiencing a splitting headache.
The headache is actually caused be the
dehydration smoking weed causes aka
cotton mouth.
When that happens sip water, dont
chug, sip slowly, have as many glasses
as it takes without drowing yourself.
you've got to pace yourself in order to
hydrate properly.
relax, going out into the cold does help because cold temperature lowers your heart rate, and body temp. Your not alone, this is something that is actually extremely common amongst stoners whether they admit it or not, i have found that every stoner i have smoked with has experienced this one time or another...
But yea it feels like your hearts going to explode on ya, its painful, you feel pops, parts of you go numb, you get a headache, you begin to shake, and you are just thinkin this is going to be such a shitty way to go out, sitting outside a shed after one blunt. been there lol...
Hope i Helped clarify the situation.