Anxiety Support Group
Anxiety is a physical condition marked by intense and persistent feelings of distress, fear, angst or dread. General anxiety caused by routine day-to-day stresses usually passes quickly and is experienced by almost everyone at one time or another. However, such feelings that linger over time and are very difficult to cope with, and which lack a clear cause, may indicate...

But seriously, I don't think it matters which one you choose first, as long as you start reading.
Crowd out that negative voice with what is being said in those books. Let the words sink in and consider that they might be true.
Good luck.
I recommend comedy novels, farce, action - any books that are funny, or interesting, or divert you from your life. I recommend music of all kinds whenever you can, movies to distract you, walks to fulfil you, gardening, playing tennis... Things with people, and things that are fun.
I know for myself that when I have an anxiety episode lasting a few days that when I come out of it I don't think anything like what I think when I'm in it. So I have to distract myself while I process the chemicals. And the more entertaining the distraction, the better it works. Once the chemicals are processed I can go back to the issue and come up with a much better set of ideas.