How does Christopher react when he sees his father’s truck parked outside of his school?

From the text:

And when I saw the van I was sick again. But I knew I was going to be sick this time so I didn’t sick all over myself and I was just sick onto the wall and the pavement, and there wasn’t very much sick because I hadn’t eaten much. And when I had been sick I wanted to curl up on the ground and do groaning.