It's funny how during an attack we feel that we cannot do the things that come naturally. As soon as the panic starts to creep up, we have a tendency to stop everything and listen in and focus on our symptoms and turn all our attention to what is happening to our bodies. You do have the ability to talk, it is just that you are concentrating so hard on how to get out of a situation when in panic, that it seems as if you cannot speak. I feel the same way sometimes. If I am in the middle of a conversation and a panic attack comes on, I feel that I cannot continue, I lose my train of thought and all I want to do is get away. Again, it is because I begin to focus on my symptoms and get distracted by them. This also happens when I am walking outside and having an attack. My main symptom is dizzyness, and I feel that my legs cannot carry me. All I want to do is stop and sit down somewhere, but I don't. My legs always seem to get me to where I am going.
Next time this happens, try to continue your conversation and you will see, your attention will shift back to what you were talking about, and the panic will begin to subside.