paninic attacks or heart races after i smoke here latey

this happened to me for the first time about a week ago... i've been consistantly enjoying weed for about the past year and until last sunday, i loved it... i smoked a miniscule amount and immediately after, i thought i was gonna have a heart attack and i ended up going to the ER... they gave me an IV w/ some ativan in it and said i had an anxiety (panic) attack... i've tried smoking twice since then and both times i felt like it was gonna happen again (i couldnt stop thinking about it even thought nothing was really happening)... how the hell can i stop this so i can go back to enjoying what this great plant was meant for!!?!?!