Why do I feel so empty all of a sudden?

I'm thirteen years old,and I've had three panic attacks in my life, one a couple months ago, and two this week. This morning, I was feeling great and normal, until PE. When we were going outside to walk the track, the coach stopped me and asked if I was okay. She said I'd been acting 'sad' lately, and I kind of panicked when I realized I had been. (Likely due to the loss of a close friend. She won't even look at me anymore.) I told her I was fine, and that I didn't know what was up, although I was in the verge of tears the whole time. (Crying is my basic reaction to even the slightest inconveniences) I walked all hohr, and I hated it, because I thought a lot, about my life, my stress from two households, school stress, and I kept repeating "my life is falling apart" over and over again even though I tried to stop. I made myself cry, and I wanted to go home, but not to my dad's, or my mom's. I was so confused. I tried to compose myself after that, but I was still in tears when I got to Social Studies, and the teacher let me go to the bathroom, where I had my third panic attack. When I came back out, I felt empty. All that class, the next one, even now after school. I can't smile, or talk loud, and my emotions aren't even working. I tried to do some things I love (drawing and reading) but I can't even force myself to do that. Why do I feel empty?