General Anxiety Disorder can include panic attacks. In truth, the various labels given to anxiety in its various guises are not very useful. For some reason psychologists and doctors like to divide anxiety in Generalized Anxiety Disorder (GAD) and Panic Disorder. The fact is, you feel what you feel and experience what you experience, and many people with anxiety also get panic attacks.
It is not surprising that anxiety and panic go hand in hand, they tend to have the same causes with a panic attack just being an extreme extension of anxiety. Ultimately anxiety and panic attacks tend to come down to low serotonin, low GABA, hyperventilation, vestibular dysfunction and trauma. People with Generalized Anxiety Disorder tend to have some of those and may even, if they are very unlucky, have both.
If you have anxiety disorder and are suffering from panic attacks it is a good idea to look at your breathing, Many people find they are suffering from Chronic Hyperventilation Syndrome.
It is also worth looking at all physical causes of anxiety, Killing Anxiety From The Roots has a lot of information on that.
You might also want to have a look at how much tryptophan you get in your diet as this can effect how much serotonin your body can produce. You could also think about the Amino Acid supplements that can raise your GABA level, which is essentially trying to do naturally what Benzodiazepines like Valium and Xanax to artificially. Which is basically to stop anxiety and panic attacks by raising GABA.