Anxiety in the workplace

I've recently realized that one of the reasons I have so much trouble working at work is that I am anxious. I don't feel safe. A person I don't know well, or trust, could walk through that door at any time and start yelling at me. This particular anxiety should go away when I am at home, or normally does, making it easier for me to focus on my work, since I no longer feel I must be alert at all times for a tiger to jump through the window and start mauling me.

Yes, it is THAT irrational.

Anyone else have this problem? What do you do for it? If I could close my door, it might be better, but I can't.