I am reading The Power of Now by Eckhart Tolle. I found these words particularly powerful:
Unease, anxiety, tension, stress, worry--all forms of fear--are caused by too much future, and not enough presence. Guilt, regret, resentment, grievances, sadness, bitterness, and all forms of nonforgiveness are caused by too much past, and not enough presence.(1)
I'm only half way through this book, but I'm finding it very powerful. It isn't specifically written for people with anxiety problems, but every word rings true for people like us.
1. Tolle E. The Power of Now: A Guide to Spiritual Enlightenment. Novato, Calif.: Namaste Publishing; 2004: 61.