What could have happened?

Hey
I've been a regular smoker for almost a year, i may not smoke every day but i do it at least 3 days a week.
I have had bad experiences when i first started smoking, because i didn't know the amount that settled me fine. In those cases i felt things as not being able to move, shaking, basically feeling like i was on another planet but not in the good way
As a regular smoker, weed has turned into another common thing in my life, i hang out with friends, drink a few beers, smoke, laugh and chill, i never get as high as i did before, it's not ''trippy'' as it was when i started, it's just relaxing and fun.
Yesterday i hanged out with two of my friends who decided to drop acid. We went riverside to chill, i decided not to take acid, so i rolled a giant joint. First i drank a beer and then smoked almost the entire joint all at once. I was feeling really high, in the good way when i, all of a sudden, started feeling like i was out of my body and very very dizzy. As i said before, i have had this experiences in my life before so it didn't frighten me, i knew nothing bad was going to happen me.
I sat real quick on the ground and told my friends i was having an intense high, but an uncomfortable one, that i was going to try to calm down. Everything got far worse from this point on, we were on a park in between the river and a street, it's a public space, so we had people on our surroundings that were making me feel unsettled, i told my friends that i'd probably start to feel beter if we went somewhere more calm. When i stood up i felt my body really heavy and the feeling that i had no control of it, even though i could move. My head was in the clouds. Around what seemed 10 minutes later we arrived to another place, again, besides the river, the difference is this place is private and you can chill without worrying about anyone. I layed down on the grass and started trembling a lot, sweating, feeling really paranoid and anxious, i could barely talk to my friends, also the feeling that i was on the edge of fainting was always there, accompanied by the unability to stand up.
My question is: Being a regular and experienced smoker, with a very high tolerance, what could have happened to me? I know it is a classical green-out episode, but i have smoked 3 or 4 joints in a few hours with friends A LOT of times (plus a lot of beer) So this isn't typical of me, i never had to measure the quantity i smoked because despite smoking a lot, i get high to certain point, i never have to worry about how much.
Now i'm as good as new, but it upsets me not knowing what could have caused this episode. I would appreciate your opinion!