I've been told recently that I have GAD. Came here to PC's Conditions and Disorders looking for a description of it (http://psychcentral.com/disorders/sx24.htm) and found their description very accurate to what I feel, especially the first 2 paragraphs. Don't know if you feel that way too. In the list of symptoms, they mention irritability, which I happen to have too, a lot!
Good luck, and I would not cancel the appointment until I knew exactly why my pdoc thinks I might have GAD.