(This example is a composite of student experiences. Any resemblance to an actual individual is purely coincidental.)
Jason sits in class feeling the restlessness in him increase. He notices that he has been bouncing his leg up and down. The sound and rhythm remind him of a distant helicopter. He is starting to feel even antsier, as if he has to get up and move around. Trouble is, he's in class and can't do that. He tries to refocus on the lecture about the wonderful world of chemistry, but he can't seem to stay focused. He also begins to notice that his recurring headache is coming back all of a sudden. "This chemistry stuff is blowing me away," he thinks to himself. His chest even feels a little tight, as it has for the past week. A wave of nausea also passes through his gut, and his heart beats a little faster, even without him being much aware of these brief changes. He wonders what is wrong with him and considers going to the doctor to get checked out.