Blacked out then vibrating heart beat?

I was walking through a friends office yesterday and all of a sudden there was an intense pressure in my head and everything started going black, like literally I couldnt see anything for a couple seconds, I didnt pass out, everything just went black, I stopped walking as soon as I realised it was happening. as soon as I could see again, there was a hard beat and immediately my heart was beating so fast it felt like it was vibrating. I laid my hand on my chest and it felt like there was a vibrator on the other side of my chest bone. I walked to my friend and she felt it too... I felt like I couldnt catch my breath. so I sat down and started trying to count the beats to see how fast it was. and I couldnt, it was beating so fast that once I got to the two syllable numbers, I couldnt keep up with it. then right about the time I was going to tell them to call EMS it stopped, with one hard beat that hurt, and then another 2 seconds later and another 2 seconds after that. then it went to a normal-ish heartbeat but it was still beating at 132 bpm my chest was sore and the left side of my neck like where you would check your pulse was also sore. so I went to the ER and they checked my heart rate and it was 127 so they put me in a wheel chair and labeled my chart "should not wait". they got me back there and the doctor said that at my age (22) it wasnt possible for it to be anything serious. But they drew blood and did a chest xray because he said the only thing it could have been at my age was a pulmonary embolism. which it wasnt. they did notice that my heart rate while I was laying down was 73 bpm but as soon as I stood up it jumped to 117 and my blood pressure went up. They sent me home saying nothing was wrong with me. And gave me a paper saying that if any of these things happen return immediately. and on the list was rapid heart rate. I walked out of the hospital with a heart rate of 120! Now let me add some back story. about a year and a half ago, I started having wierd sensations in my heart, the ER did a holter monitor and they said I was having 6-7 PVC's an hour, and that sleeping my heart rate was 150. they did an ekg it was fine, they did an echo cardiogram and it came back normal too, but ever sense then I have episodes when my heart rate jumps to about 120-140bpm with me not doing anything strenuous that would warrant it to be that high, and its always coupled with the sensation that I cant catch my breath.

I dont like the fact that I am 22 and was sent home from the ER with them basically telling me it is normal for you everything to go black and for your heart to be beating so fast that it feels like a vibrator.

Does anyone have any ideas???