will i snap?

That is the question: will I snap?
Tonight I was talking to someone on IM. It is like hanging up on someone on IM if you just leave without telling them. So I told them I'd be right back so I could take my dog to the bathroom, which my mom asked me to do, and when I got back she had taken the computer, even though she knew I was talking to someone, which has happened on multiple occasions.

Maybe I'm just easier to anger lately, but I got angrier and angrier as thirty minutes went by (she told me she'd take five) and I knew the person I was talking to was probably gone. So I very calmly said, "Mom, next time will you tell me if you're going to take the computer without me knowing so I can say good bye to people?"

She said, "I didn't think I was going to take this long."
"All the same," I said, still calmly, "please tell me. It's really rude of me to just leave. And I was talking about something I cared about."
"She has signed off," my mom said. "She said [etc.]."
"Please don't read my IM conversation."
"You little sh*t, you can't tell me what to do."
"Please don't call me names."
"Well don't act like my mom! You can't tell me what to do!"
"That doesn't justify you calling me a name."

I was very calm. But I didn't feel calm inside. I am very good at making the way I'm feeling very different from the way I act, though. I feel a turmoil of confusion. Some part of me says I'm exaggerating this, making anyone that reads this believe it's worse than it is just so I can get some sort of pathetic validation for the anger I feel. Some parts of me knows I'm not exaggerating. Some part of me doesn't understand why, if my mom loves me, she does these things to me. Some part of me believes I'm provoking it (I am). I need consistency. If you love me, don't hurt me. That's the way it's supposed to be.

I am angry.
It is okay to be angry.
It is okay for me to feel this way.
I will be angry for a minute or two.