A little anxiety can be helpful. After all, it's good to be aware of the world around you. But how much is too much? And how do you tell if anxiety is getting the better of you -- or a loved one? Seth Gillihan, a psychology professor at the University of Pennsylvania, has the answers. We also hear from Alicia Clark, a psychologist in Washington, D.C., who says anxiety can be a powerful tool for everyday life. Plus, we'll give you real-time tips to help a friend who's having a panic attack.