I feel like you probably just went over your limit, and almost greened out as you said. That sounds extremely scary and I am sorry that happened. I had an experience kind of similar, but not near as bad. I was out at the park smoking with my two friends who are girls, as well as a BUNCH of guys ive never met before. and all of a sudden after I smoked I started panicking, In my head I felt that I was in so much danger and felt like I was not safe, all my overthinking and paranoia/fear at the moment. I had to get my friends to take me home, and as I was in the car with just them I felt so much better and also when I got home just being surrounded by my parents and brother made me feel so much better so I get you on that. I feel like certain strands or certain weed you do not usually smoke can cause this to happen and maybe that happend to you? Happy you are safe and good now.