ANTs are "Automatic Negative Thoughts" and the phenomenon works something like this according to the founder of Cognitive Behavior Therapy (CBT), Dr. Beck. Beck wrote that basically you can't help this army of negative thoughts from entering your brain, they just do. You find yourself saying "I'm a failure" and "I can't do this" and "I suck." These thoughts influence what you then actually do, which is to beat yourself up over the thoughts and then you get depressed. The behavior follows, which includes things like wanting to sleep twelve hours a day and isolate from the world, then that feeds back even more into a rumination mood where all you can think about is how bad you feel. It's depression and it's a vicious cycle. Add anxiety and it's essentially unlive-able. You can't function.
I spent part of yesterday in the ER, because my heart was racing and I felt jittery all over like a rubber band that someone was constantly thwanging. I thought I was going to have a heart attack. They gave me an EKG. I was amazed to find that I was fine and all my vitals checked out. So my physical symptoms, it was all just the anxiety. Amazing what anxiety can cause, physically. They gave me an Atavan to calm me and watched me for two hours and then I came home.