My mercurial child and his meltdowns

O started his acting class today, and I couldn't have hoped for a better start. First off he came out of school in a good mood, secondly he was fine going to his new class, even though he had no prior knowledge he was going. A surprise and he took it in stride, that was good. He got a little worried when I wasn't sure where the class was, but stayed calm. We found the building and the room, and he went in without hesitation, I was shocked! He didn't worry about where I was, or what I was doing or anything he might normally do. About halfway through he came out, I worried about what was next, but it was just a potty break. He was so excited to get back, he wouldn't even wait for me to finish in the bathroom and raced back to class. It was at this point I became happy with myself and my son, we had found an activity and place he really enjoyed. I jumped the gun a bit. Next thing I know, he comes bursting out the door with the teacher chasing after telling him not to run out of the room. He's screaming, "I hate this class, I want to kill everyone, I want to kill myself!" I should note here that my son is not homicidal nor suicidal, he just has emotional issues, as in he can't control his. Once he loses his emotions like this whether it be from anger, anxiety, or fear, it becomes very difficult to rein back in. Apparently he was upset because he didn't want to be an angry bear, he wanted to be the laughing happy chipmunk. I kid you not, this is what he was upset about. He goes back in, and shortly returns just as angry, because now he has lost the privilege to play the bear. So now he is angry about being a bear, angry with himself for losing control, and angry that he doesn't get to participate, everything has built up now so that he runs and hides in a corner between a garbage can and the wall just sobbing and screaming. Two eleven year old girls there for another class watch this whole thing and inform me that he is in the right place and is going to make a great actor, they are serious about this. At this point he is neither calming down nor stopping screaming, so I physically pick him up and take him a flight of stairs up, away from everything to try and calm him down. Of course he screams out that I'm hurting him as I carry him up, always love the implications of child abuse. He says he just wants to go home and he never wants to see this place again, I ask that we talk to the teacher first. The teacher says he was great the whole time and she wasn't sure what happened, but that she would love to have him back next week. She said they were taking turns with the bear and chipmunk, and she's not sure why he ran, because she was actually going to have him be a chipmunk. O just keeps crying. pleading to go home NOW! We finally leave, and the entire 8 minute walk back to the car, he yells and complains, asking why I would sign him up for such a class, why didn't I tell him (we had discussed it the night before), and my personal favorite, how it was the worst day ever! O is a master of hyperbole, even better than Bill Walton. I just told him we weren't talking about it until later. After a few minutes driving in the car, he's calm, and tells me he is hungry and just wants to go home and have pasta for dinner. It is at this point I remember that most of his meltdowns, can be traced back to contributing issues, i.e. he's hungry or tired. I ask if that was part of his problem, he says yes, and agrees that he liked the class and will go back again next week. I actually stayed calm through all of this, I don't always, I often get frustrated with the irrationality of it and him. It goes better when I am calm, it just gives me a headache and need for a stiff drink or two later. You watch, next week will be the best day ever and why can't he come to the class more, it's never a dull day with O, I can tell you that.