rapid cardiac ritm

This is the second time this happens to me.i have been having like palpitations like for 3 years Now,but that occur like maybe 2 times a week or sometimes 2 or three times 2 months and like that ,not like an everyday thing.But in 06' i was working HARD WITH A LOT OF STREES  AND ONE AFTERNOON WHEN I WAS COOKING MY HEART  STARTED BEATING FAST AND HARD THAT I COULDNT EVEN BREATH ,IT LAST LIKE FOR 3 MINUTES AND I CAN SAY THAT IT WAS LIKE 100 BEATS OR MORE PER MINUTE.TODAY THAT HAPPENED TO ME AGAING BUT WITH THA DIFFERIENCE THAT I DONT CONSIDER BEEN STREESING NOW AND ACTUALLY I WAS IN THE CAR WITH MY BOYFRIEND AND HE WAS DRIVIN.I THINK I DROVE THRU SOME HOLE OR SUMTHING LIKE THAT BECAUSE WHEN I JUMPED THATS WHEN MY HEART STARTED BEATING LIKE THAT AGAING HARD AND FAST  I COULDNT BREATH I WAS SO SCARED THAT I THOUGHT I WAS GONNA DIE.I SAW THE DOCTOR LIKE 1 MONTH AGO AND HE EVEN PUT THE HOLTER MONITOR AND EVERYTHING CAME UP GOOD.BUT IM WORRY.WHAT SHOULD I DO NOW..PLEASE I NEED AND ANSWER.THANKS.