It could happen to students cramming for exams, people working long hours or just about anyone burning the candle at both ends: Something tells you to take a break. Watch some TV. Have a candy bar. Goof off, tune out for a bit and come back to the task at hand when you’re feeling better. After all, you’re physically exhausted. But a new study suggests the urge to refresh (or just procrastinate) is — well — all in your head.