I have struggled with anxiety on and off for a number of years. I am pretty sure it's genetic, as my dad did and I think my mom had periods of it as well. I would say that 95% of the time for me, it's not an issue, but then it creeps back in, mostly at night. The darkness magnifies what would - in the daylight - seem trivial or at least manageable - into almost terrifying possibilities.
If anxiety equals lack of faith, then I believe I stand in good company. Look at Christ in the Garden of Gethsamane: the AGONY in the Garden. He agonized - in worry, fright, anticipation - of what stood before Him. He clearly knew that pain and betrayal awaited Him, and He was anxious.
Telling a "worrier" not to to worry is like telling water not to be wet. It isn't going to happen. We all have worries and most of us manage them quite nicely, but those of us with anxiety can't always get our brains to shut out those very real worries. Children get hurt, money runs out, pain occurs, people die: all very real things. And some of us are anxious about the emotional toil it takes.
I have faith. I believe, I believe, I believe. And I am anxious. More than that, I believe Christ stands with me in my anxiety, not scolding me for lack of faith, but in deep compassion and empathy. I will continue to battle the anxiety, but I am also assured that I can do all things through Christ who strengthens me - even when I'm afraid.