Could be your personality. Have you ever thought about talking to a guidance counseler or psychologist? Everyonce in a while, I can feel 'nervous'. I do something I like to refocus my mind...go out and take pictures, play a video game, watch the news. Just something to change gears in my head.

But if this happens even when you don't smoke, you really should talk to someone. If unchecked, it can grow worse.